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Brain tissue potassium in normal and potassium depleted rats
Life Sciences, Vol . 21, pp . 1851-1856 Printed is the U .S .A .
Pergaaioa Prasa
BRAIN TISSUS POTASSIUM IN NORMAL AND POTASSIUM DSPLSfED &1TS $. $. Nattie Department of Physiology, Dartmouth Medical School, Haaover, NH 03755 (Received in final form November 8, 1977) Summar~
The potassium concentration of muscle, brainstam and diencaphalon were studied is normal and potassium-depleted rats . With 13Z depletion of muscle potassium there was a 2 .1Z and 2.8Z decrease in brainstem and diencephalon tissue potassium respectively . With 34x depletion of muscle potassium there was a 1.9x and 4 .OZ decrease in brainstem and diencephalon tissue potassium. These small decreases is regional brain tissue potassium could be related to observed functional alterations in the potassium depleted rat, i .e ., altered cerebrospinal fluid bicarbonate regulation sad altered control of the pattern of breathing and of body temperature regulation . Brain tissue potassium (R) is thought to be maintained within narrow limits even in the face of large variations in plasma values and whole body balance (1,2) . With chronic R depletion in the rat,alteratioae in certain physiological functions have been observed . Cerebrospinal fluid (CSF) bicarbonate regulation is altered (3) as is the breathing pattern (4,5) and body temperature regulation (6) . Oae possible locus for the R depletion effect on all of these functions resides in brain tissue . As recent work has demonstrated a small decreasé in choroid plexus tissue R is R depleted rate (7) this study evaluates the effects of R depletion on muscle, brainstem and diencephalon tissue R. Methods All rats in the study were specific pathogen free females purchased from Hilltop Laboratory Animal Inc., Scottdale, Pennsylvania . They were housed in a temperature and humidity controlled room and fed standard rat chow and water ad lib unless on the dietary protocol described below. R depletion was produced by feeding the experimental groups a diet low in R (Taklad Mills, Madison, Wisconsin) . This diet has been shown to produce a aignific~t sad relatively stable R depletion on days 15-18 of the protocol (3) . Three e~ periments ware performed. In the first experiment, twelve animals were randomly and equally divided into low R and control groups . After the low R animals had been on the diet for 17 days, both groups were sacrificed and brain tissue sodium and potassium analysis was performed as described below. Ln the second experiment, aiztean animals were randomly and equally divided into low R sad control groups . These animals were sacrificed after the low R animals had been on the R deficient diet for 23 days . The control animals in both of these experiments were treated ezactly like the low R experimental animals except for the fact that they were fed normal rat chow . 1851
1852
Brain Tissue R in R Depletion
Vol . 21, No . 12, 1977
As the R depleted animals have a metabolic alkalosis (3), the third experiment was performed to verify that the metabolic alkalosis per aé was not affecting brain tissue R. Eighteen animals were randomly divided into 3 groups ; control with ao injections, control with mock iajectiona ; and animals injected with base to produce metabolic alkalosis . All eighteen animals had been fed normal rat chow and water ad lib . The injection protocol has been described before including the measurement of arterial acid-base parameters on blood sampled from tmanesthetized rats to verify the presence of a metabolic alkalosis (3) . The experimental group was injected i .p . 4 times once every 1~ hours with a solution containing NaHC03, 0.155 M and RC1, 0 .005 M. Sacrifice occurred 2-3 hours after the last injection . The control animals with mock injection were handled and received an abdominal needle puncture in a manner exactly like that of the injected group except that no material was actually injected . the animals with no injection were not handled until sacrifice. At the time of sacrifice the animals of these three experiments were weighed and tail length was measured . Each animals was decapitated with a guillotine and the whole brain was quickly removed and dissected using the anatomical landmarks of Glawinski and Iveraen (8) to isolate and remove the diencephalon and brainstem. Muscle samples were taken from the neck in representative aaimala of each group . The brain and muscle tissue samples were weighed wet, dried to stable weight at 95 ° C, weighed dry then digested in 2 ml of 0 .78 N HN03 in sealed vials . Sodium and potassium concentration of the acid extract was measured using .a flame photometer . Results All animals appeared to be in good health at the time of experimentation. It has been shown that in animals fed the low K diet for 15-18 days, the rate of body weight gain is decreased (3) predominantly due to decreased body fat (9) as skeletal growth, reflected by tail length measurements, is unaffected (3) . These findings were verified is the first ezperiment . Table 1 . Body Weight and Tail Length of Normal and Potassium Depleted Rata with 17 and 23 Days of Dietary Treatment . Values are Mean t SEM. Body Weight
(g)
Tail Length (cm)
Initial
Final
Initial
Final
Control (N~6)
149 .0 3 .0
227 .5 7 .0
14 .6 .1
17 .1 .2
R depleted (N~6) 17 days on diet
153.7 3.6
202 .0 7 .4
14 .6 .3
16 .8 .2
NS
P< .O1
NS
NS
Control (N~8)
162 .4 1.4
235.5 3.1
15 .2 .1
17 .6 .1
R depleted (N~8) 23 days on diet
158.4 1 .6
179 .5 2 .7
14 .8 .2
16 .8 .2
NS
P< .O1
P< .05
P< .O1
Vol . 21, No . 12, 1977
Brain Tissue R in R Depletion
1853
The initial mean body weight and the initial and final mean tail lengths The were not significantly different comparing control and low R values . In the second final mean body weights were significantly different (P<0 .01) . experiment with 23 days on the low R diet, there was an effect on tail length as well as a more pronounced effect on body weight . The final mesa body weight after 23 days on the diet was 23 .7X lean than controls as compared to And there was a small but significant 11 .22 lean after 17 days on the diet . The effect (P<0 .05) on the change in tail length after 23 days on the diet . results indicated that with 23 days on the diet starting at an initial body weight of 150-160 gms there might be additional effects of R depletion on protein metabolism sad growth, as effect previously described in severe R depletion (10) . The main results of the first two experiments are ehovn in Table 2 . The data for the two control groups were not significantly different and were Tab le 2 . Sodium and Potassium Concentration in Muscle and Brain Regions of Narmal and Potassium Depleted Rata . The Control Group Data are Pooled . The Data are Rapreased as Mean Values t SBM. Muscle (mM/Rg wet wt .)
Brainatem (mM/Rg wet wt .)
Diencephalon (mM/Rg wet wt .)
Na
R
Na
R
ZH 20
Na
R
XH 20
Control (N~14)
25 .3 2.1
109 .5 2 .1
51 .7 1.0
90 .3 0 .6
74 .9 0 .2
60 .2 1.8
97 .0 1 .1
81 .0 0 .3
R depleted (N-6) 17 days on diet
--
95 .1+ 1 .9
50 .0 1.0
88 .4+ 0.9
75 .0 0 .2
57 .2 2 .7
94 .3+ 1.3
82 .0 0 .3
R depleted (N~8) 23 days on diet
31 .6 + 1 .5
72 .0+ 0 .8
53 .6 1.6
88 .6+ 0.6
74 .9 0 .3
57 .8 1.6
93 .1+ 82 .3 1.3 0 .3
+ P< .05 compared to control therefore pooled . With 17 days on the low R diet and 13X depletion of muscle R, there was a 2 .1Z decrease in brainetem tissue R (P<0 .05) and a 2.8X decrease in dieacephalic tissue R(P< .05) . With 23 days on the lov R diet and 34X depletion of muscle R there was a 1 .9X decrease in brainstem tissue R These changes (P<.05) and 4.0X decrease in diencephalic tissue R(P< .O1) . The were small, but they were reproducible and statistically significant . accompanying changes in brainßtem and diencephalic tissue Na were variable and not statistically significant, and there was no effect in either experiment on brain water content . The results of the third experiment 'showed that . there was no effect of metabolic alkalosis per aé over 6 hre on brainstem and dieacephalic tissue R. Control and metabolic alkalosic group mean brainstem tissue R (± SBM) were 89 .3 ± 0.7 and 88 .4 t 0.5 respectively, a 1X decrease that was not atatietically significant . Control sad metabolic alkalosic mean dieacephalic tissue R were 96 .7 t 0.5 and 97 .0 t 1 .7 respectively . The changes in Na were variable sad not significant, sad there was no effect of the metabolic alkalosis on brain water content ; brainstem water content being 75 .1X t 0.3 and diencephalic water content being 81 .7X ± 0 .3 . Thin control for metabolic allcaloeis occurred over 6 hra while the R depletion protocols took 17-23 days .
1854
Brain Tissue R is K Depletion
Vol . 21, No . 12, 1977
Thus it is as imperfect control . However, given that after 6 hra there are demonstrable and significant chmmgea is plasma and CSF acid-base balance (4) and that it has proven difficult to produce in the rat a chronic metabolic alkalosis without some effect oa R balance, the results at the least show that acute metabolic alkalosis in plasma and CSF of the rat does not affect brain tissue R. Mscuseion The main finding of this study, that in K depleted rats there is a small but significant decrease in brainstem and diencephalon tissue R, is is disagreement with the findings of Bradbury and Rleeman (2) . These authors reported that is rabbits with dietary K depletion similar in severity to that of this report, there was no detectable change in whole brain tissue R. There are two apparent possible explanations for this discrepmmcy in results . First, there could be a species difference in the degree of brain tissue R regulation . That Johaasoa _et _al . (7) have reported small but significant decreases in ctwroad plexus tissue R in the rat with dietary R depletion of a severity similar to this study and that of Bradbury and Rleemaa (2) is consistent with this eaplaaation . Second, the experiments might differ in regard to some factor other than R. For example, hyponatremia appears to be a situation in which brain tissue K is not regulated as completely as it is when the stress is simply that of altered K balance (1) . Ia the results of Bradbury and Rleemmm In (2) there did not appear to be mmy aignificmmt change in serum or CSF Na . the experiments of this report serum or CSF Na was not measured . But in previous experiments in animals treated in the same mmmner the mean (t SEI~ serum Na of control and K depleted animals was 144 .9 t 0 .9 and 137 .6 ± 1.9 respectively and the CSF values were 151 .5 t 0 .5 and 144 .5 t 2 .7 respectively (3) . Thus, the rata with dietary K depletion in this study were probably However, the degree of chronic hyponatremia that has been mildly hyponatremic . shown as necessary to alter measurably brain tissue R has been more severe than that observed with this protocol . More specifically ü: pats with chronic hyponatremia (serum Na ~ 130 mM/1) more severe than in the animals of this R depletion protocol there was no observable chmmge in brain tissue Na, R or H2O content (1) . these observations together with the fact that in this report there was no change in brainstem mmd diencephalon water content with K depletion suggests but does not prove that the observed decrease in brainstem mmd diencephalon tissue R is due not to the hyponatremia but to the depletion of K. While it is not clear why rabbits do not exhibit a chmmge is brain tissue R and rats do when stressed with the same degree of R depletion, it is apparent that even in the rat there is mm impressive degree of tissue K regulation . With 13X sad 34X muscle R depletion, brainstem R decreases roughly 2X is both cases while diencephalon R decreases roughly 3 .OX and 4 .OX respectively . If these differences is tissue R of the brainstem and diencephalon with different degrees of muscle K depletion hope significance biologically the possibility ie raised that the diencephalon, a region that has been suggested to have a more permeable blood brain barrier (11), does not regulate R as well as the brainstem. How could the small decrease in brairetem and diencephalon tissue R affect CSF bicarbonate regulation (3) or neuronal function as observed in the altered pattern of breathing (4,5) and the altered body temperature regulation (6)? Oae possible mesas would be through an alteration in excitable cell membrane function . In skeletal muscle of the K depleted dog (12) and rat (12, 13) hyperpolarization has been observed indicating that the ratio of eztra-
Vol . 21, No . 12, 1977
Brain Tissue R is R Depletion
1855
cellular td intracellular K, Re/Ri, has decreased, i .e ., that in R depletion the chmmge in extracellular R is greater proportionally than the change in intracellular R. Using values for CSF R obtained is the earlier similar studies (3), the tissue R values of this study and asatmtiag a value of 0 .15 for the eatracellular space of the brain, the ratio Re/Ri calculated for brain is also decreased in R depletion though the changes are small. The small degree of hyperpolarization could accotent in part for the functional alterations. This interpretation is speculative and measurements of brain cell resting membrane potential would be necessary to prove it correct . Alternatively the small decrease in cell R could alter cell metabolic pathways as R is mm importnt regulator of many key enzymes (14) . Neuronal function could then be indirectly altered as the altered cell enzyme activity affected central energy or neurotransmitter metabolism (14) . Or R ~cotild directly affect neurotrmmsmitter metabolism . Studies is vitro have shows that R is important in norepinephrine release (15) mmd uptake (16) . And in studies in R depleted rat heart _ia vivo the pattern of results observed suggest that NE release may be inhibited (17) . press relationships of R and NE are intriguing since cats (18) mmd rats (Nattie, unpublished observations) treated with reserpine have alterations in breathing patterns similar to those observed in R depleted animals, i .e ., a large tidal volume mmd a slow respiratory frequency and NE is postulated as a neurotransmitter important in the regulation of body temperature (19) . (Acknowledgements . Supported by National Heart and Ltmg Institute Grmmt HL 02888 mmd by Young Pulmonary Investigator Research Grmmt HL 18351.) References 1. 2. 3 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
15 . 16 . 17 . 18 . 19 .
R. RATZMAN mmd H .M . PAPPIUS, Brasa Electrolytes and Fluid Metabolism , Williams and Wilkina, Baltimore (1973) . M.W .B . BRAIR;URY and C.R . RLEEMAN, Am. J. Phyaiol . 213 519-528 (1967) . E .E . NATTIE sad S .M . TENNEY, Am . _J.Phyaiol . 231 579-587 (1976) . E .B . NATTIE and S .M . TENNEY, _Am. _J . Phyaiol. _231 588-592 (1976) . E .E . NATTIE, J. Appl . Phyaiol . (in press) . E.E . NATTIE, The Physiologist 17, 295 (abstract) (1974) . C.E . JOHANSON, D .J . REED mmd D. M. WOODBURY, J. Phyaiol. 241 359-372, (1974) . J . GLOWINSRI and L.L . IVERSON, J . Neurochem. 13 655-665 (1966) . M . HOHENEGGER, W. MARRTL and B . RUDAS~rs Arch 351 331-338 (1974) . A .B . GüSTAFSON, L. SHEAR mmd G.J . GABUZDA, J . _Lab . Clin . Med. 82 287296 (1973) . W.H . OLDENDORF, Permeability of the blood-brain barrier, in : The Nerwus System , ed . by D.B . TOWER, Vol . I: The Basic Neurosciences, Raven, New York (1975) . G.L . BILBREY, L . HERB IN, N .W . CARTER and J .P . RNOCHEL, J. Clin . Invest . 52 3011-3018 (1973) . H .D . BOLTS and B. LUDERITZ, Pfhtigers Arch . 301 43-49 (1968) . H .S . MAKER, D .D . CLARKS and A.L . LAJTHA, Intermediary metabolism of carbohydrates and amino acids, in : Basic Neurochemistry , ed . by G.J . SIEGAL, R.W . ALBERS, R. RATZMAN mmd B .W . AGRANOFP, Little Brown, Boston (1976) . J .D . COORS and D.M .J . QUASTEL, _J . Phyaioi . _228 435-458 (1973) . T .D . WHITE mmd D. M. PATON, Biochem. Biophys . Acts 266 116-127 (1972) . L .R . RRAKOFF, Circ . _Res . _30 608-615 (1972) . M.J . MILLER, Ph .D . Thesis, Dartmouth College (1973) . W. FELDBERG and V.J . IATTI, Br . J . Pharmac . Qtemother . 31 152-161 (1967) .
Pergaaioa Prasa
BRAIN TISSUS POTASSIUM IN NORMAL AND POTASSIUM DSPLSfED &1TS $. $. Nattie Department of Physiology, Dartmouth Medical School, Haaover, NH 03755 (Received in final form November 8, 1977) Summar~
The potassium concentration of muscle, brainstam and diencaphalon were studied is normal and potassium-depleted rats . With 13Z depletion of muscle potassium there was a 2 .1Z and 2.8Z decrease in brainstem and diencephalon tissue potassium respectively . With 34x depletion of muscle potassium there was a 1.9x and 4 .OZ decrease in brainstem and diencephalon tissue potassium. These small decreases is regional brain tissue potassium could be related to observed functional alterations in the potassium depleted rat, i .e ., altered cerebrospinal fluid bicarbonate regulation sad altered control of the pattern of breathing and of body temperature regulation . Brain tissue potassium (R) is thought to be maintained within narrow limits even in the face of large variations in plasma values and whole body balance (1,2) . With chronic R depletion in the rat,alteratioae in certain physiological functions have been observed . Cerebrospinal fluid (CSF) bicarbonate regulation is altered (3) as is the breathing pattern (4,5) and body temperature regulation (6) . Oae possible locus for the R depletion effect on all of these functions resides in brain tissue . As recent work has demonstrated a small decreasé in choroid plexus tissue R is R depleted rate (7) this study evaluates the effects of R depletion on muscle, brainstem and diencephalon tissue R. Methods All rats in the study were specific pathogen free females purchased from Hilltop Laboratory Animal Inc., Scottdale, Pennsylvania . They were housed in a temperature and humidity controlled room and fed standard rat chow and water ad lib unless on the dietary protocol described below. R depletion was produced by feeding the experimental groups a diet low in R (Taklad Mills, Madison, Wisconsin) . This diet has been shown to produce a aignific~t sad relatively stable R depletion on days 15-18 of the protocol (3) . Three e~ periments ware performed. In the first experiment, twelve animals were randomly and equally divided into low R and control groups . After the low R animals had been on the diet for 17 days, both groups were sacrificed and brain tissue sodium and potassium analysis was performed as described below. Ln the second experiment, aiztean animals were randomly and equally divided into low R sad control groups . These animals were sacrificed after the low R animals had been on the R deficient diet for 23 days . The control animals in both of these experiments were treated ezactly like the low R experimental animals except for the fact that they were fed normal rat chow . 1851
1852
Brain Tissue R in R Depletion
Vol . 21, No . 12, 1977
As the R depleted animals have a metabolic alkalosis (3), the third experiment was performed to verify that the metabolic alkalosis per aé was not affecting brain tissue R. Eighteen animals were randomly divided into 3 groups ; control with ao injections, control with mock iajectiona ; and animals injected with base to produce metabolic alkalosis . All eighteen animals had been fed normal rat chow and water ad lib . The injection protocol has been described before including the measurement of arterial acid-base parameters on blood sampled from tmanesthetized rats to verify the presence of a metabolic alkalosis (3) . The experimental group was injected i .p . 4 times once every 1~ hours with a solution containing NaHC03, 0.155 M and RC1, 0 .005 M. Sacrifice occurred 2-3 hours after the last injection . The control animals with mock injection were handled and received an abdominal needle puncture in a manner exactly like that of the injected group except that no material was actually injected . the animals with no injection were not handled until sacrifice. At the time of sacrifice the animals of these three experiments were weighed and tail length was measured . Each animals was decapitated with a guillotine and the whole brain was quickly removed and dissected using the anatomical landmarks of Glawinski and Iveraen (8) to isolate and remove the diencephalon and brainstem. Muscle samples were taken from the neck in representative aaimala of each group . The brain and muscle tissue samples were weighed wet, dried to stable weight at 95 ° C, weighed dry then digested in 2 ml of 0 .78 N HN03 in sealed vials . Sodium and potassium concentration of the acid extract was measured using .a flame photometer . Results All animals appeared to be in good health at the time of experimentation. It has been shown that in animals fed the low K diet for 15-18 days, the rate of body weight gain is decreased (3) predominantly due to decreased body fat (9) as skeletal growth, reflected by tail length measurements, is unaffected (3) . These findings were verified is the first ezperiment . Table 1 . Body Weight and Tail Length of Normal and Potassium Depleted Rata with 17 and 23 Days of Dietary Treatment . Values are Mean t SEM. Body Weight
(g)
Tail Length (cm)
Initial
Final
Initial
Final
Control (N~6)
149 .0 3 .0
227 .5 7 .0
14 .6 .1
17 .1 .2
R depleted (N~6) 17 days on diet
153.7 3.6
202 .0 7 .4
14 .6 .3
16 .8 .2
NS
P< .O1
NS
NS
Control (N~8)
162 .4 1.4
235.5 3.1
15 .2 .1
17 .6 .1
R depleted (N~8) 23 days on diet
158.4 1 .6
179 .5 2 .7
14 .8 .2
16 .8 .2
NS
P< .O1
P< .05
P< .O1
Vol . 21, No . 12, 1977
Brain Tissue R in R Depletion
1853
The initial mean body weight and the initial and final mean tail lengths The were not significantly different comparing control and low R values . In the second final mean body weights were significantly different (P<0 .01) . experiment with 23 days on the low R diet, there was an effect on tail length as well as a more pronounced effect on body weight . The final mesa body weight after 23 days on the diet was 23 .7X lean than controls as compared to And there was a small but significant 11 .22 lean after 17 days on the diet . The effect (P<0 .05) on the change in tail length after 23 days on the diet . results indicated that with 23 days on the diet starting at an initial body weight of 150-160 gms there might be additional effects of R depletion on protein metabolism sad growth, as effect previously described in severe R depletion (10) . The main results of the first two experiments are ehovn in Table 2 . The data for the two control groups were not significantly different and were Tab le 2 . Sodium and Potassium Concentration in Muscle and Brain Regions of Narmal and Potassium Depleted Rata . The Control Group Data are Pooled . The Data are Rapreased as Mean Values t SBM. Muscle (mM/Rg wet wt .)
Brainatem (mM/Rg wet wt .)
Diencephalon (mM/Rg wet wt .)
Na
R
Na
R
ZH 20
Na
R
XH 20
Control (N~14)
25 .3 2.1
109 .5 2 .1
51 .7 1.0
90 .3 0 .6
74 .9 0 .2
60 .2 1.8
97 .0 1 .1
81 .0 0 .3
R depleted (N-6) 17 days on diet
--
95 .1+ 1 .9
50 .0 1.0
88 .4+ 0.9
75 .0 0 .2
57 .2 2 .7
94 .3+ 1.3
82 .0 0 .3
R depleted (N~8) 23 days on diet
31 .6 + 1 .5
72 .0+ 0 .8
53 .6 1.6
88 .6+ 0.6
74 .9 0 .3
57 .8 1.6
93 .1+ 82 .3 1.3 0 .3
+ P< .05 compared to control therefore pooled . With 17 days on the low R diet and 13X depletion of muscle R, there was a 2 .1Z decrease in brainetem tissue R (P<0 .05) and a 2.8X decrease in dieacephalic tissue R(P< .05) . With 23 days on the lov R diet and 34X depletion of muscle R there was a 1 .9X decrease in brainstem tissue R These changes (P<.05) and 4.0X decrease in diencephalic tissue R(P< .O1) . The were small, but they were reproducible and statistically significant . accompanying changes in brainßtem and diencephalic tissue Na were variable and not statistically significant, and there was no effect in either experiment on brain water content . The results of the third experiment 'showed that . there was no effect of metabolic alkalosis per aé over 6 hre on brainstem and dieacephalic tissue R. Control and metabolic alkalosic group mean brainstem tissue R (± SBM) were 89 .3 ± 0.7 and 88 .4 t 0.5 respectively, a 1X decrease that was not atatietically significant . Control sad metabolic alkalosic mean dieacephalic tissue R were 96 .7 t 0.5 and 97 .0 t 1 .7 respectively . The changes in Na were variable sad not significant, sad there was no effect of the metabolic alkalosis on brain water content ; brainstem water content being 75 .1X t 0.3 and diencephalic water content being 81 .7X ± 0 .3 . Thin control for metabolic allcaloeis occurred over 6 hra while the R depletion protocols took 17-23 days .
1854
Brain Tissue R is K Depletion
Vol . 21, No . 12, 1977
Thus it is as imperfect control . However, given that after 6 hra there are demonstrable and significant chmmgea is plasma and CSF acid-base balance (4) and that it has proven difficult to produce in the rat a chronic metabolic alkalosis without some effect oa R balance, the results at the least show that acute metabolic alkalosis in plasma and CSF of the rat does not affect brain tissue R. Mscuseion The main finding of this study, that in K depleted rats there is a small but significant decrease in brainstem and diencephalon tissue R, is is disagreement with the findings of Bradbury and Rleeman (2) . These authors reported that is rabbits with dietary K depletion similar in severity to that of this report, there was no detectable change in whole brain tissue R. There are two apparent possible explanations for this discrepmmcy in results . First, there could be a species difference in the degree of brain tissue R regulation . That Johaasoa _et _al . (7) have reported small but significant decreases in ctwroad plexus tissue R in the rat with dietary R depletion of a severity similar to this study and that of Bradbury and Rleemaa (2) is consistent with this eaplaaation . Second, the experiments might differ in regard to some factor other than R. For example, hyponatremia appears to be a situation in which brain tissue K is not regulated as completely as it is when the stress is simply that of altered K balance (1) . Ia the results of Bradbury and Rleemmm In (2) there did not appear to be mmy aignificmmt change in serum or CSF Na . the experiments of this report serum or CSF Na was not measured . But in previous experiments in animals treated in the same mmmner the mean (t SEI~ serum Na of control and K depleted animals was 144 .9 t 0 .9 and 137 .6 ± 1.9 respectively and the CSF values were 151 .5 t 0 .5 and 144 .5 t 2 .7 respectively (3) . Thus, the rata with dietary K depletion in this study were probably However, the degree of chronic hyponatremia that has been mildly hyponatremic . shown as necessary to alter measurably brain tissue R has been more severe than that observed with this protocol . More specifically ü: pats with chronic hyponatremia (serum Na ~ 130 mM/1) more severe than in the animals of this R depletion protocol there was no observable chmmge in brain tissue Na, R or H2O content (1) . these observations together with the fact that in this report there was no change in brainstem mmd diencephalon water content with K depletion suggests but does not prove that the observed decrease in brainstem mmd diencephalon tissue R is due not to the hyponatremia but to the depletion of K. While it is not clear why rabbits do not exhibit a chmmge is brain tissue R and rats do when stressed with the same degree of R depletion, it is apparent that even in the rat there is mm impressive degree of tissue K regulation . With 13X sad 34X muscle R depletion, brainstem R decreases roughly 2X is both cases while diencephalon R decreases roughly 3 .OX and 4 .OX respectively . If these differences is tissue R of the brainstem and diencephalon with different degrees of muscle K depletion hope significance biologically the possibility ie raised that the diencephalon, a region that has been suggested to have a more permeable blood brain barrier (11), does not regulate R as well as the brainstem. How could the small decrease in brairetem and diencephalon tissue R affect CSF bicarbonate regulation (3) or neuronal function as observed in the altered pattern of breathing (4,5) and the altered body temperature regulation (6)? Oae possible mesas would be through an alteration in excitable cell membrane function . In skeletal muscle of the K depleted dog (12) and rat (12, 13) hyperpolarization has been observed indicating that the ratio of eztra-
Vol . 21, No . 12, 1977
Brain Tissue R is R Depletion
1855
cellular td intracellular K, Re/Ri, has decreased, i .e ., that in R depletion the chmmge in extracellular R is greater proportionally than the change in intracellular R. Using values for CSF R obtained is the earlier similar studies (3), the tissue R values of this study and asatmtiag a value of 0 .15 for the eatracellular space of the brain, the ratio Re/Ri calculated for brain is also decreased in R depletion though the changes are small. The small degree of hyperpolarization could accotent in part for the functional alterations. This interpretation is speculative and measurements of brain cell resting membrane potential would be necessary to prove it correct . Alternatively the small decrease in cell R could alter cell metabolic pathways as R is mm importnt regulator of many key enzymes (14) . Neuronal function could then be indirectly altered as the altered cell enzyme activity affected central energy or neurotransmitter metabolism (14) . Or R ~cotild directly affect neurotrmmsmitter metabolism . Studies is vitro have shows that R is important in norepinephrine release (15) mmd uptake (16) . And in studies in R depleted rat heart _ia vivo the pattern of results observed suggest that NE release may be inhibited (17) . press relationships of R and NE are intriguing since cats (18) mmd rats (Nattie, unpublished observations) treated with reserpine have alterations in breathing patterns similar to those observed in R depleted animals, i .e ., a large tidal volume mmd a slow respiratory frequency and NE is postulated as a neurotransmitter important in the regulation of body temperature (19) . (Acknowledgements . Supported by National Heart and Ltmg Institute Grmmt HL 02888 mmd by Young Pulmonary Investigator Research Grmmt HL 18351.) References 1. 2. 3 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
15 . 16 . 17 . 18 . 19 .
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