Microelectrode study of intracellular pH in frog skin: dependence on serosal chloride.

Replacement of external chloride has been known to reduce Na+ transport across whole frog skin. However, the sidedness and mechanism of the phenomenon have been unclear. In the present study, transepithelial current (IT), transepithelial resistance (RT), and basolateral membrane potential measured both with reference micropipettes (psi sc) and pH-selective microelectrodes (EscH) were monitored in isolated epithelial sheets from frog skin; removal of the underlying dermis facilitates ionic exchange across the basolateral membranes. The intracellular hydronium ion activity (acH) was 58 +/- 4 nM (means +/- SE) when the extracellular hydronium activity was 25 +/- 1 nM under base-line conditions. This measurement is equivalent to an intracellular pH (pHc) of 7.24 +/- 0.03 at an extracellular pH of 7.60 +/- 0.01, in reasonable agreement with estimates obtained by 31P- and 19F-nuclear magnetic resonance (NMR) analyses of frog skin. Complete replacement of mucosal Cl- by gluconate had variable effects on tissue current and resistance from preparation to preparation. The same ionic substitution on the serosal side uniformly produced a prompt reversible decrease in IT, increase in RT, and a substantial membrane depolarization of the short-circuited skins. In most of the preparations, the depolarization was preceded by a small hyperpolarization of 0.5-3.5 mV. The replacement of serosal Cl- also produced a fall in intracellular hydronium ion activity of 33 +/- 10 nM. The present date are consistent with the concept that serosal replacement of Cl- alkalinizes the cells by either favoring HCO3- entry or blocking HCO3- exit through a Cl- HCO3 antiport at the basolateral membrane.(ABSTRACT TRUNCATED AT 250 WORDS)