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Correlations of Na+−Li+ exchange activity with Na+ and Li+ binding and phospholipid composition inerythrocytes of hypertensive and normotensive individuals
AIH 1995; 8:122A-123A
POSTERS: Cellular and Membrane Transport D2
Dl INCREASED ERYnlROCYTE RUBIDIUM LEAK AS A MARKER OF SALT SENSITIVITY IN THE RAT? LZkllll, Z Dobdov6., and J Kunes, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic. Most of rat strains exhibit bioott pressure rise if their salt intake is sufficiently increased prior to sexual maturation. The extent of salt-induced blood pressure elevation is, however, highly variable so that particular strains are classified as salt-sensitive: or salt-resistant. A reliable cellular marker of salt sensitivity is still missing. Our studies of ion transport in red blood cells suggested that the search for the marker of salt sensitivity should be focused on augmented passive membrane permeability for various monovalent cations, namely on Increased Na" and Rbr leaks. Our findings indicate that 1) alterations of Nat and Rb" leaks were often dissociated in experimental hypertension (e.g, DOCA-salt hypertensive rats or hereditary hypertriglyceridemic rats) in which Na+ leak was increase(J without changes of Rb" leak, 2) Na+ leakbut not Rb" leak cosegregated with blood pressure in recombinant inbred strains (SHR x BN), 3} Rb+ leak but not Na+ leak was elevated in all three examined salt-sensitive strains (Dahl SSlJr rats, Sabra SBH rats, Prague SHR/Ipcv rats), and 4) Rb" leak was not modified by dietary salt intake although Na+ leak was usually augmented insalthypertensive animals. Thus ouabain- andfurosemide-resistant sodium leak seems to be associated with high blood pressure in spontaneous forms of genetic hypertension whereas increased Rb! leak can be considered as a potential marker ofthesaltsensitivity in the rat. Supponcd by t're rescarelr grant Z128 (CzeclJ Millistry ofHealt").
DIFFERENT PLATELET CALCIUM HANDLING IN SPONTANEOUS AND SALT-DEPENDENT FORMS OF GENETIC HYPERTENSION IN nIE RAT. J Zieha', J Kund*, and M-A Devynck. Pharmacology, CHU Necker, CNRS URA 1482, Paris, France, and ·Institute of Physiolo~, Czech Academy of Sciences, Prague, Czech Repubhc. The relationship of ~tosolic free calcium levels to blood pressure was studied in three different rat strains WIth genetlc hypertension in which blood pressure elevation is either spontaneous (Lyon rats) or salt-induced (Dahl and Sabra rats). tlsiDlt Fura-z technique, cytosolic free calcium (fCaH)i) was determined in both resting and thrombin-stimulated platelets ofsalthypertensive Dahl and Sabra rats as well as in Lyon hypertensive rats. Resting platelet [Ca2+Ji was elevated oi:l1~ in Lyon hypertensive rats in which it correlated posi~lVely with diastolic blood pressure (reflecting the alterations of systemic resistance). In contrast, no [Ca2+]i increase was found in both models ofsalt-dependent hypertension which were characterized by the clear association of platelet [Ca2 +)i with pulse (and systolic) pressures but not with diastolic pressure. Thrombin-induced [Ca2+]i increment was augmented in Lyon hypertensive rats, unchanged in Dahl rats andeven decreased insalthypertensive Sabra rats. The initial rate of thrombin-induced Mn2 + entry through Mn2 +permeable Ca2+ channels was suppressed by high salt intake in salt-resistant but not in salt-sensitive rats. In conclusions, spontaneous and salt-dependent forms of genetic hypertension differ substantially in the relationship of platelet fCa 2+Ji to particular hemodynamic components of blood pressure. Thrombininduced Mn2+ entry was increased in Lyon rats with spontaneous hypertension as well as in salt hypertensive Dahl and Sabra rats compared to their controls. Supported by the researd: grant 2128 (Czech Millistry of Health).
KeyWords:
Rb: leak, Na+ leak, erythrocytes, rat saltsensitivity, Dahl, Sabra, SHR
D3
cytosolic calcium, thrombin response, platelets, Dahl, Sabra, Lyon strains
D4
CORRELATIONS OF Na+-ti+ EXCHANGE ACTIVITY WITH Na+ AND Li+ BINDING AND PHOSPHOLIPID COMPOSITION INERYTHROCYTES OFHYPERTENSIVE AND NORMOTENSIVE INDIVIDUALS. Y Chi, DM de Freitas, M Sikora, and VK Bansal. It Loyola University, Chicago, It. Enhanced Na'-Li" exchange activity has been reported in red blood cells (RBCs) of essential hypertensive patients relative to that found in RBCs of normotensive individuals. To understand the factors responsible for the fast rates of Na +-Li" exchange in RBCs of essential hypertensive patients, we used blood samples from ten hypertensive patients and ten matched normotensive individuals. We measured the kinetic parameters (V.Id, Vrw , and K..J for RBC Na+·Li+ exchange by using atomic absorption spectrophotometry; and we IISed 2lNa and 'Lincclear magnetic resonance (NMR) relaxatlon methods to measure Na" and Li' binding, respectively, to RBe membranes, and IIp NMR spectroscopy to measure the membrane phospholipid composition. We found significant differences between the two groups for the affinity of Na+ for theRBC membrane (193 ± 65 mM for hypertensives vs. 296 ± 71 mM for normotensives, P < 0.02), and the kinetic parameters ofRBC Na+·Li+ exchange (VIId, V".... and K", were 0.32 ± 0.08.0.64 ± 0.18 mmol Li+/L RBC.hl', and 162 ± 59 mM for hypertensives vs, 0.21 ± 0.06, 0.32 ± 0.14 mmol Li' IL RBC.hr, and 86 ± 69 mM for normotenslves, P < 0.02). No statistically significant differences were found for Li" binding and phospholipid composition. The Na+ binding constants were negatively correlated (r ::: -0.4, p < 0.05) with the rates ofRBC Na'-Ll" exchange. We conclude that changes in the RBC membrane of "irertensive patients results in weaker Na" binding to the membrane. and in faster rates of RBe Na +-Ll" exchange. KeyWords:
Key Words:
ion transport, membrane binding. NMR
DIETARY CALCIUM DOES NOT AFFECT ALTERED MONOVALENT ION TRANSPORT IN SHR. SN Orlov. SR Kuznetsov, P Dumas. J Tremblay" and P Hamet", Centre de recherche Hotel-Dieu de Montreal, Universite de Montreal, Montreal, Quebec, Canada Numerous data indicate that abnormalities of plasma membrane ion transporters are involved in long-term maintenance of elevated BP in SHR and essential hypertensives (EH). The mechanism of the antihypertensive effect of dietary Ca in SHR and in salt-sensitive EH is still unknown. In this study, we examined whether dietary Ca modifies monovalent ion transport in RBC. Four-week-old male SHR and WKY rats were kept ona 2%saltandlow Ca (LC, 0.25%) or high Ca (HC. 2.5%) diet for 9 weeks, Inward and outward Na,K cotransport (InCO. OuteD) and passive permeability to K and Na (PK• PNJ were measured as ouabain-resistant, bumetanide-sensitive (InCO, OutCO) or ouabain-bumetanide-resistant (PK• PNJ l6Rb influx and 22Na efflux (mmol'J RBC·!hr"l).
WKY-LC SHR·LC WKY·HC SHR·HC
(lIeo
ouco
Pv
2.47±O.O8 3.06:1:0.08" 2.85%0.05. 132%0.15
O.67:tO.I;t~
0.63:tO.04 0.79:1:0.05
1.56:1:0.21 0.79%0.04. 1.12:tO.lO
O.76:l:O.04 0.84%0.05
P"'n 1.9Y#).I2 2.25:1:0.10 2.45%0.29 2.45:W.l8
·p
Both InCO and OutCO were increased whereas P" and PN• were not altered in SHR as compared to WKY. These results are concordant with dab obtained previously in rats kept on a normal salt diet (0.4%). Dietary Ca did not modifY Na and K transport. suggesting that these ion transport pathways are not involved in theantihypertensive effeet ofCa in thediet. KeyWords:
calcium. diet, Na-K cotransport, erythrocytes, spontaneous hypertension ~.
POSTERS: Cellular and Membrane Transport D2
Dl INCREASED ERYnlROCYTE RUBIDIUM LEAK AS A MARKER OF SALT SENSITIVITY IN THE RAT? LZkllll, Z Dobdov6., and J Kunes, Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic. Most of rat strains exhibit bioott pressure rise if their salt intake is sufficiently increased prior to sexual maturation. The extent of salt-induced blood pressure elevation is, however, highly variable so that particular strains are classified as salt-sensitive: or salt-resistant. A reliable cellular marker of salt sensitivity is still missing. Our studies of ion transport in red blood cells suggested that the search for the marker of salt sensitivity should be focused on augmented passive membrane permeability for various monovalent cations, namely on Increased Na" and Rbr leaks. Our findings indicate that 1) alterations of Nat and Rb" leaks were often dissociated in experimental hypertension (e.g, DOCA-salt hypertensive rats or hereditary hypertriglyceridemic rats) in which Na+ leak was increase(J without changes of Rb" leak, 2) Na+ leakbut not Rb" leak cosegregated with blood pressure in recombinant inbred strains (SHR x BN), 3} Rb+ leak but not Na+ leak was elevated in all three examined salt-sensitive strains (Dahl SSlJr rats, Sabra SBH rats, Prague SHR/Ipcv rats), and 4) Rb" leak was not modified by dietary salt intake although Na+ leak was usually augmented insalthypertensive animals. Thus ouabain- andfurosemide-resistant sodium leak seems to be associated with high blood pressure in spontaneous forms of genetic hypertension whereas increased Rb! leak can be considered as a potential marker ofthesaltsensitivity in the rat. Supponcd by t're rescarelr grant Z128 (CzeclJ Millistry ofHealt").
DIFFERENT PLATELET CALCIUM HANDLING IN SPONTANEOUS AND SALT-DEPENDENT FORMS OF GENETIC HYPERTENSION IN nIE RAT. J Zieha', J Kund*, and M-A Devynck. Pharmacology, CHU Necker, CNRS URA 1482, Paris, France, and ·Institute of Physiolo~, Czech Academy of Sciences, Prague, Czech Repubhc. The relationship of ~tosolic free calcium levels to blood pressure was studied in three different rat strains WIth genetlc hypertension in which blood pressure elevation is either spontaneous (Lyon rats) or salt-induced (Dahl and Sabra rats). tlsiDlt Fura-z technique, cytosolic free calcium (fCaH)i) was determined in both resting and thrombin-stimulated platelets ofsalthypertensive Dahl and Sabra rats as well as in Lyon hypertensive rats. Resting platelet [Ca2+Ji was elevated oi:l1~ in Lyon hypertensive rats in which it correlated posi~lVely with diastolic blood pressure (reflecting the alterations of systemic resistance). In contrast, no [Ca2+]i increase was found in both models ofsalt-dependent hypertension which were characterized by the clear association of platelet [Ca2 +)i with pulse (and systolic) pressures but not with diastolic pressure. Thrombin-induced [Ca2+]i increment was augmented in Lyon hypertensive rats, unchanged in Dahl rats andeven decreased insalthypertensive Sabra rats. The initial rate of thrombin-induced Mn2 + entry through Mn2 +permeable Ca2+ channels was suppressed by high salt intake in salt-resistant but not in salt-sensitive rats. In conclusions, spontaneous and salt-dependent forms of genetic hypertension differ substantially in the relationship of platelet fCa 2+Ji to particular hemodynamic components of blood pressure. Thrombininduced Mn2+ entry was increased in Lyon rats with spontaneous hypertension as well as in salt hypertensive Dahl and Sabra rats compared to their controls. Supported by the researd: grant 2128 (Czech Millistry of Health).
KeyWords:
Rb: leak, Na+ leak, erythrocytes, rat saltsensitivity, Dahl, Sabra, SHR
D3
cytosolic calcium, thrombin response, platelets, Dahl, Sabra, Lyon strains
D4
CORRELATIONS OF Na+-ti+ EXCHANGE ACTIVITY WITH Na+ AND Li+ BINDING AND PHOSPHOLIPID COMPOSITION INERYTHROCYTES OFHYPERTENSIVE AND NORMOTENSIVE INDIVIDUALS. Y Chi, DM de Freitas, M Sikora, and VK Bansal. It Loyola University, Chicago, It. Enhanced Na'-Li" exchange activity has been reported in red blood cells (RBCs) of essential hypertensive patients relative to that found in RBCs of normotensive individuals. To understand the factors responsible for the fast rates of Na +-Li" exchange in RBCs of essential hypertensive patients, we used blood samples from ten hypertensive patients and ten matched normotensive individuals. We measured the kinetic parameters (V.Id, Vrw , and K..J for RBC Na+·Li+ exchange by using atomic absorption spectrophotometry; and we IISed 2lNa and 'Lincclear magnetic resonance (NMR) relaxatlon methods to measure Na" and Li' binding, respectively, to RBe membranes, and IIp NMR spectroscopy to measure the membrane phospholipid composition. We found significant differences between the two groups for the affinity of Na+ for theRBC membrane (193 ± 65 mM for hypertensives vs. 296 ± 71 mM for normotensives, P < 0.02), and the kinetic parameters ofRBC Na+·Li+ exchange (VIId, V".... and K", were 0.32 ± 0.08.0.64 ± 0.18 mmol Li+/L RBC.hl', and 162 ± 59 mM for hypertensives vs, 0.21 ± 0.06, 0.32 ± 0.14 mmol Li' IL RBC.hr, and 86 ± 69 mM for normotenslves, P < 0.02). No statistically significant differences were found for Li" binding and phospholipid composition. The Na+ binding constants were negatively correlated (r ::: -0.4, p < 0.05) with the rates ofRBC Na'-Ll" exchange. We conclude that changes in the RBC membrane of "irertensive patients results in weaker Na" binding to the membrane. and in faster rates of RBe Na +-Ll" exchange. KeyWords:
Key Words:
ion transport, membrane binding. NMR
DIETARY CALCIUM DOES NOT AFFECT ALTERED MONOVALENT ION TRANSPORT IN SHR. SN Orlov. SR Kuznetsov, P Dumas. J Tremblay" and P Hamet", Centre de recherche Hotel-Dieu de Montreal, Universite de Montreal, Montreal, Quebec, Canada Numerous data indicate that abnormalities of plasma membrane ion transporters are involved in long-term maintenance of elevated BP in SHR and essential hypertensives (EH). The mechanism of the antihypertensive effect of dietary Ca in SHR and in salt-sensitive EH is still unknown. In this study, we examined whether dietary Ca modifies monovalent ion transport in RBC. Four-week-old male SHR and WKY rats were kept ona 2%saltandlow Ca (LC, 0.25%) or high Ca (HC. 2.5%) diet for 9 weeks, Inward and outward Na,K cotransport (InCO. OuteD) and passive permeability to K and Na (PK• PNJ were measured as ouabain-resistant, bumetanide-sensitive (InCO, OutCO) or ouabain-bumetanide-resistant (PK• PNJ l6Rb influx and 22Na efflux (mmol'J RBC·!hr"l).
WKY-LC SHR·LC WKY·HC SHR·HC
(lIeo
ouco
Pv
2.47±O.O8 3.06:1:0.08" 2.85%0.05. 132%0.15
O.67:tO.I;t~
0.63:tO.04 0.79:1:0.05
1.56:1:0.21 0.79%0.04. 1.12:tO.lO
O.76:l:O.04 0.84%0.05
P"'n 1.9Y#).I2 2.25:1:0.10 2.45%0.29 2.45:W.l8
·p
Both InCO and OutCO were increased whereas P" and PN• were not altered in SHR as compared to WKY. These results are concordant with dab obtained previously in rats kept on a normal salt diet (0.4%). Dietary Ca did not modifY Na and K transport. suggesting that these ion transport pathways are not involved in theantihypertensive effeet ofCa in thediet. KeyWords:
calcium. diet, Na-K cotransport, erythrocytes, spontaneous hypertension ~.