Acetylcholine‐evoked potassium transport in the isolated guinea‐pig pancreas

Abstract

SUMMARYIn this study, K+ concentration was measured in effluent samples from superfused guinea-pig pancreatic pieces in control conditions and during stimulation with ACh, employing the technique of flame photometry. ACh (10-7_10-5 M) evoked a dose-dependent and sustained increase in K+ concentration in the effluent (K+ release). The removal of Ca2+ from the superfusing medium and the addition of 10-4 M EGTA caused a significant (P < 0.05) reduction in the ACh-evoked K+ efflux. Replacement of extracellular Cl-in the superfusing physiological salt solution with NO3-abolished the ACh-induced K+ efflux. In contrast, when Cl-was replaced with Br-, ACh still evoked marked K+ release. Pretreatment of pancreatic segments with the loop diuretic furosemide (10-4 M) resulted in an inhibition of K+ efflux elicited by ACh. Stimulation of pancreatic segments with the Na+-K+-ATPase inhibitor ouabain (10-3 M) caused a large efflux of K+. In the continuous presence of ouabain, ACh application elicited no further change in the K+ release. The results indicate that ACh-evoked K+ release from guinea-pig pancreatic segments is sensitive to ouabain, Cl-, furosemide and extracellular Ca2' and that only the basal efflux is augmented by ouabain. The findings provide further evidence that a diuretic-sensitive coupled Na+-K+-Cl-cotransport system operates in the guinea-pig pancreas, as it does in other similar transporting epithelia, to bring about K+ mobilization.