Potassium ions and the secretion of insulin by islets of Langerhans incubated in vitro

Abstract

1. A method was devised for the isolation of islets of Langerhans from rabbit pancreas by collagenase digestion in order to study the influx and efflux of K+ in islets during insulin secretion. 2. Glucose-induced insulin release was accompanied by an increased rate of uptake of 42K+ by the islets of Langerhans, though this was not the case for secretion in response to tolbutamide. Ouabain significantly inhibited the uptake of 42K+ by islet tissue. 3. No significant increase in the rate of efflux of 42K+ was demonstrated during active insulin secretion. 4. Slices of rabbit pancreas were incubated in media of different K+ content, and rates of insulin release were determined. Alteration of the K+ concentration of the medium between 3 and 8mm had no effect on the rate of insulin release by pancreas slices. However, decrease of the K+ concentration to 1mm resulted in inhibition of secretion in response to both glucose and to tolbutamide. Conversely, an increase in K+ concentration increased rates of insulin release in response to both these stimuli. 5. It is concluded that, though unphysiological concentrations of K+ may influence the secretion of insulin, fluxes of K+ in the islets do not appear to be important in the initiation of insulin secretion.