Effect of external sodium on intracellular chloride activity in the surface cells of frog gastric mucosa

Abstract

The intracellular chloride activity and its dependence on ionic substitutions in the bathing media was studied in individual surface cells of resting gastric mucosa using conventional and Cl⁻ selective microelectrodes. When the tissue was perfused with control NaCl-Ringer the cell membrane p.d.'s, cell-lumen (Ψ_cm) and cell-serosa (Ψ_cs) were −40.9±0.6 mV and −66.8±0.5 mV (n=175) respectively specitively and the p.d. measured by the Cl⁻ selective microelectrodes across the serosal membrane (Ψ ^Cl-_cs ) averaged −32.4±0.7 mV (n=138). From these values an intracellular Cl⁻ activity (a ^Cl−_c ) of 15.3 mmol/l can be estimated. The data indicate that chloride ion is distributed close to equilibrium at the luminal membrane while it is accumulated by an energy requiring step at the serosal membrane. Reduction (2 mmol/l) or absence of chloride from the luminal bath did not result in any detectable change ofa ^Cl−_c ; on the other hand, after removal of Cl⁻ from the serosal bath the intracellular Cl⁻ activity fell to 7.1 mmol/l.

When the tissue was exposed to serosal Na⁺-free Ringer (Na⁺ replaced by choline or TMA), although thea ^Cl−_c remained unaffected, a marked reduction of the electrochemical gradient for Cl⁻ at the serosal membrane was observed.

These data indicate that: (i) chloride is accumulated in the surface cells against its electrochemical potential difference at the serosal membrane; (ii) the luminal membrane has a negligible conductance to Cl⁻, while the serosal membrane represents a conductive pathway to chloride; (iii) the uphill entry of chloride at the serosal membrane seems to be, at least partially, Na⁺-dependent.