Whole-cell currents in isolated resting Necturus gastric oxynticopeptic cells

Abstract

1. Necturus gastric mucosa secretes Cl- actively across the gastric glands which are composed almost entirely of acid- and enzyme-secreting oxynticopeptic cells. Single channel studies on Necturus oxynticopeptic cells have shown that the basolateral membrane possesses multiple K(+)-selective channels but no observable Cl- channels while the apical membrane has Cl- channels but no observable K+ channels. To relate these channel properties to the conductance of the whole cell we have investigated the macroscopic membrane currents with conventional whole-cell patch-clamp techniques. 2. When bathed in amphibian Ringer solution, gastric oxynticopeptic cells had a membrane resistance of 47.8 +/- 2.8 M omega and a membrane capacitance of 75.5 +/- 2.7 pF (n = 82). This gave a specific membrane resistance of 3260 +/- 160 omega cm2 (n = 82). Reversal potentials of the oxynticopeptic cells were -13.8 +/- 1.2 mV (n = 45) for an intracellular Cl- concentration ([Cl-]i) of 42 mM and were significantly more negative -24.4 +/- 3.1 mV (n = 31, P < 0.001) for [Cl-]i = 22 mM. 3. In the absence of ATP in the pipette solution, there was an 80% reduction of the whole-cell current with a typical half-time (t1/2) of 5 min. The run-down was not observed when the pipette solution contained 4 mM ATP. 4. A slow and voltage-independent inhibition of 80% of the whole-cell currents occurred after addition of NPPB (35 microM). Ba2+ (10 mM) produced a reversible inhibition of 20% of the total current. Together, 35 microM NPPB and 10 mM Ba2+ eliminated 95% of the whole-cell currents. These data suggest that in the resting oxynticopeptic cells Cl- carried the major fraction of the current while K+ ions carried only a small fraction. 5. Total replacement of Cl- in the pipette and bath solution by gluconate- increased the membrane resistance to 751 +/- 104 M omega (n = 53) and shifted the reversal potential to -38.1 +/- 2.8 mV (n = 53). 6. Increasing the bath K+ concentration from 6 to 91 mM activated a current which had a high selectivity for K+ over choline+, Li+, Na+, Rb+ and Cs+ and was independent of Cl-. The activation of this K+ current (IK*) by high external K+ was not seen with ATP-free pipette solution. 7. Ba2+ or Cs+ had a voltage-dependent blocking effect of this inward K+ current. Ouabain (1 mM) or SCH 28080 (200 microM), specific inhibitors of the Na+,K(+)-ATPase and H+,K(+)-ATPase, had no effect.(ABSTRACT TRUNCATED AT 400 WORDS)