Acetylcholine-evoked potassium release in the mouse pancreas

Abstract

Mouse pancreatic segments were superfused with physiological saline solutions and the K+ concentration in the effluent was measured by flame photometry. Acetylcholine (ACh) evoked a dose-dependent and transient increase in the K+ concentration in the effluent (K+ release). The removal of calcium (Ca2+) from the superfusing solution and addition of 10(-4) M-EGTA (ethyleneglycol-bis-(beta-amino-ethylether)N,N'-tetraacetic acid) caused a significant reduction in the ACh-elicited K+ outflow. Pre-treatment of pancreatic segments with the 'loop diuretics' (furosemide, piretanide and bumetanide; all 10(-4) M) resulted in uptake of K+ into the tissue segments. The diuretics also caused a marked reduction in the ACh-induced K+ release. Replacement of chloride (Cl-) in the physiological salt solution by nitrate (NO3-), sulphate (SO42-) or iodide (I-) caused K+ uptake and a significant reduction in the ACh-evoked K+ release. However, when Cl- was replaced by bromide (Br-) the response to ACh was virtually unaffected. When sodium (Na+) was replaced by lithium (Li+) ACh did not evoke K+ release but instead K+ uptake was observed. However, when Tris+ was substituted for Na+ ACh evoked a very small K+ release. Pre-treatment of pancreatic segments with 10(-3) M-ouabain resulted in a marked sustained K+ release. In the continuing presence of ouabain ACh induced a further increase in K+ outflow. Pre-treatment of the preparation with 10 mM-tetraethyl-ammonium (TEA) caused a small transient increase in K+ efflux, but TEA had virtually no effect on the secretagogue-evoked changes in effluent K+ concentration. The results suggest the presence of a diuretic-sensitive Na+-K+-Cl- co-transport system in the mouse pancreatic acinar membrane.