Microelectrode study of intracellular pH in frog skin: dependence on serosal Cl-

Replacing external Cl- reduces Na+ transport across frog skin, but the sidedness and mechanisms have been unclear. We have monitored current (l/sub T/), resistance (R/sub T/) and basolateral membrane potential, both with reference micropipettes (psi/sup sc/) and pH-selective microelectrodes (E/sub H//sup sc/), in short-circuited epithelial sheets isolated from frog skins; removal of the dermis facilitates basolateral exchange. Intracellular pH was 7.25 +- 0.03 (mean +- SE) when the pH of the external Cl- Ringer's solution was 7.60 +- 0.01, in reasonable agreement with estimates from 31P and 19F NMR analyses. Complete mucosal replacement of Cl- by gluconate had variable effects on l/sub T/ and R/sub T/. However, serosal Cl- substitution uniformly increased R/sub T/ and markedly decreased l/sub T/, absolute value phi/sup sc/ and absolute value E/sub A//sup sc/. The membrane depolarization was usually preceded by a small hyperpolarization (0.5-3.5 mV). The serosal Cl- replacement also produced an intracellular alkalinization of 0.4 +- 0.1 U. These data suggest that: (1) serosal Cl- substitution alkalinizes the cells by either enhancing HCO- entry or blocking HCO- loss through a basolateral Cl/HCO antiport, and (2) the fall in absolute value phi/sup sc/ and l/sub T/ may partly reflect inhibition of apical Na+ entry, produced indirectly by membrane depolarization resulting from altered basolateral ionic conductances