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Gastric potential difference measurements influenced by changes in pH
April
poorly
CORRESPONIIENCE
1989
defined
fraction
of bile.
Once
the elements
and
systems
responsible for the secretion of the BSIF are better identified we should be in a position to test the zonal distribution of the system(s). In summary, more and more studies are describing zonal differences in transport, intracellular transit time. and biotransformation of bile acids. Preliminary evidence also indicates that there are differences in the location of rate-limiting enzymes involved in bile acid synthesis. Whether some or all of these differences are regulated by availability of substrates or by phenotypic expression of rate limiting proteins, or by both, still has to be defined. But, it certainly looks heterogeneous to us. IORGE ). GUMUCIO.
M.D.
PETER G. TRABER. M.D.
Depurtment of Internal Medicine (11 ID) Veterans Administration IMedical Center 2215 Fuller Road Ann Arbor. Michigan 48105 1. Traber PG. Chiranale J, Grumucio JJ. Physiologic significance and regulation of hepatocellular heterogeneity. Gastroenterology 1988:95:1130-43. 2. Baumgartner, et al. Am J Physiol 1987;252:G114-9. 3. Groothuis. et al. Am J Physiol 1982;243:G455-62. 4. Hepatology 1988:8:174 (A #582). 5. Princen. et al. Hepatology 1988:8:167 (A #5.55).
Gastric Potential Difference Measurements Influenced by Changes in pH Dear Sir: We read with interest the paper of Patronella et al. (1) concerning in vivo measurement of gastric mucus pH under changing luminal acidity and prostaglandin E, pretreatment. The otherwise superb experiments were combined with gastric transmural potential difference measurements (PD) to assess the gastric mucosal integrity (1). The PD measurements were, how ever, performed without regard to the influence of changing luminal pH on the measured transmural PD. Changes in luminal pH will result in a changing magnitude of the liquid junction PD existing between the PD measuring probe in the stomach and the luminal contents (2-4). This will result in a change in the measured PD. which does not necessarily reflect changes in the transmural PD, but possibly only changes in the liquid junction PD (2-4). The transmural gastric PD reported in the paper by Patronella et al. (1) is subject to substantial pH-induced liquid junction artifacts.
1231
We recommend that measurements of transmural gastric PD should be performed in situations with unchanged gastric pH, or should be corrected for the pH-induced changes (3.4). LISELOTTE HQJGAARD. M.D.
JENS B. S~LOW. M.D.. Ph.D. Department of Clinical Physiolog!, Bispebjerg Hospital DK 2200 Copenhagen, Denmark Patronella CK. Vanek I. Bowen JC. In viva measurement of gastric mucus pH in canines: effect of high luminal acidity and prostaglandin E,. Gastroenterology 1988;95:612-8. Barry PH, Diamond JM. Junction potentials. electrode standard potentials and other problems in interpreting electrical properties of membranes. J Membr Biol 1970:3:93-122. Read NW, Fordtran JS. The role of intraluminal junction potentials in the generation of gastric potential difference in man. Gastroenterology 1979;76:932-8. Hdjgaard L, Andersen JR, Krag E. A new method for measurement of the electrical potential difference amoss the stomach wall. Stand J Gastroenterol 1987;22:847-58. Reply. It is recognized that liquid junction potentials may contribute significantly to the PD measured across the gastric wall as suggested by Read and Fordtran in 1978 (1). These authors demonstrated how the liquid junction potential increased with increasing luminal acidity, estimating a +lO mV difference at a luminal HCl concentration of 100 mEq/L (the maximal HCl concentration in our experiment) when 1 M KC1 electrodes were used. Extrapolating from their data using 1 M KC1 electrodes, the magnitude of junction potential between 100 mEq of HCI per liter (pH 1.0) and 80 mEq of HCI per liter (pH 1.1) is -1-2 mV, clearly insignificant compared with the change in transmural potential from -56.4 to -31.8 mV measured. Thus. the relative constancy of liquid junction potentials between the tvvo groups being compared allows the same conclusion. In addition, our histologic data correlated well with the change in transmural potential observed between the two groups. IOHN C. BOWEh’, M.D. CHRISTOPHER K. PATR0NELL.A
Ochsner Clinic I 5 14 feflerson Highnray Net\, Orleans. Louisiana
hl.11
70121
1. Read NW. Fordtran JS. The role of intraluminal junction potentials in the generation of gastric potential difference in man. Gastroenterology 1979;76:937-8.
poorly
CORRESPONIIENCE
1989
defined
fraction
of bile.
Once
the elements
and
systems
responsible for the secretion of the BSIF are better identified we should be in a position to test the zonal distribution of the system(s). In summary, more and more studies are describing zonal differences in transport, intracellular transit time. and biotransformation of bile acids. Preliminary evidence also indicates that there are differences in the location of rate-limiting enzymes involved in bile acid synthesis. Whether some or all of these differences are regulated by availability of substrates or by phenotypic expression of rate limiting proteins, or by both, still has to be defined. But, it certainly looks heterogeneous to us. IORGE ). GUMUCIO.
M.D.
PETER G. TRABER. M.D.
Depurtment of Internal Medicine (11 ID) Veterans Administration IMedical Center 2215 Fuller Road Ann Arbor. Michigan 48105 1. Traber PG. Chiranale J, Grumucio JJ. Physiologic significance and regulation of hepatocellular heterogeneity. Gastroenterology 1988:95:1130-43. 2. Baumgartner, et al. Am J Physiol 1987;252:G114-9. 3. Groothuis. et al. Am J Physiol 1982;243:G455-62. 4. Hepatology 1988:8:174 (A #582). 5. Princen. et al. Hepatology 1988:8:167 (A #5.55).
Gastric Potential Difference Measurements Influenced by Changes in pH Dear Sir: We read with interest the paper of Patronella et al. (1) concerning in vivo measurement of gastric mucus pH under changing luminal acidity and prostaglandin E, pretreatment. The otherwise superb experiments were combined with gastric transmural potential difference measurements (PD) to assess the gastric mucosal integrity (1). The PD measurements were, how ever, performed without regard to the influence of changing luminal pH on the measured transmural PD. Changes in luminal pH will result in a changing magnitude of the liquid junction PD existing between the PD measuring probe in the stomach and the luminal contents (2-4). This will result in a change in the measured PD. which does not necessarily reflect changes in the transmural PD, but possibly only changes in the liquid junction PD (2-4). The transmural gastric PD reported in the paper by Patronella et al. (1) is subject to substantial pH-induced liquid junction artifacts.
1231
We recommend that measurements of transmural gastric PD should be performed in situations with unchanged gastric pH, or should be corrected for the pH-induced changes (3.4). LISELOTTE HQJGAARD. M.D.
JENS B. S~LOW. M.D.. Ph.D. Department of Clinical Physiolog!, Bispebjerg Hospital DK 2200 Copenhagen, Denmark Patronella CK. Vanek I. Bowen JC. In viva measurement of gastric mucus pH in canines: effect of high luminal acidity and prostaglandin E,. Gastroenterology 1988;95:612-8. Barry PH, Diamond JM. Junction potentials. electrode standard potentials and other problems in interpreting electrical properties of membranes. J Membr Biol 1970:3:93-122. Read NW, Fordtran JS. The role of intraluminal junction potentials in the generation of gastric potential difference in man. Gastroenterology 1979;76:932-8. Hdjgaard L, Andersen JR, Krag E. A new method for measurement of the electrical potential difference amoss the stomach wall. Stand J Gastroenterol 1987;22:847-58. Reply. It is recognized that liquid junction potentials may contribute significantly to the PD measured across the gastric wall as suggested by Read and Fordtran in 1978 (1). These authors demonstrated how the liquid junction potential increased with increasing luminal acidity, estimating a +lO mV difference at a luminal HCl concentration of 100 mEq/L (the maximal HCl concentration in our experiment) when 1 M KC1 electrodes were used. Extrapolating from their data using 1 M KC1 electrodes, the magnitude of junction potential between 100 mEq of HCI per liter (pH 1.0) and 80 mEq of HCI per liter (pH 1.1) is -1-2 mV, clearly insignificant compared with the change in transmural potential from -56.4 to -31.8 mV measured. Thus. the relative constancy of liquid junction potentials between the tvvo groups being compared allows the same conclusion. In addition, our histologic data correlated well with the change in transmural potential observed between the two groups. IOHN C. BOWEh’, M.D. CHRISTOPHER K. PATR0NELL.A
Ochsner Clinic I 5 14 feflerson Highnray Net\, Orleans. Louisiana
hl.11
70121
1. Read NW. Fordtran JS. The role of intraluminal junction potentials in the generation of gastric potential difference in man. Gastroenterology 1979;76:937-8.