Ionic requirements in histamine-evoked potassium efflux in guinea pig pancreas

Abstract

Guinea pig pancreatic segments were superfused during 10 min with physiological saline solutions containing 10-6 M acetylcholine (ACh) or histamine (10-3-10-6 M) and the potassium concentration in the effluent ([K+](o)) was measured by flame photometry. Histamine evoked a transient increase in [K+](o). The removal of calcium from the superfusing solution and addition of 10-4 M EGTA caused a significant reduction in the histamine-evoked potassium outflow. Replacement of chloride (Cl-) in the physiological salt solution by nitrate (NO3-) caused a significant reduction in the histamine-evoked potassium release. However, when Cl- was replaced by bromide (Br-) the response to histamine was unaffected. Pre- treatment of pancreatic segments with furosemide (10-4 M) or ouabain (10-3 M) caused a marked reduction in the histamine-induced potassium release. The results suggest that ionic requirements in histamine-evoked potassium release are the same as those in acetylcholine-evoked potassium efflux.