Potassium-induced insulin release and voltage noise measurements in single mouse islets of Langerhans

Insulin release and membrane potential fluctuations in response to increased extracellular potassium [K+]o have been measured in single perifused islets of Langerhans from normal mice. An increase in [K+]o from 5 mM to 50 mM induced a transient insulin release with a peak at about 1 min. The peak value was [K+]o-dependent but the half-time t1/2 for the decline was constant at nearly 1 min. 2.5 mM cobalt completely inhibited the potassium-induced stimulation of insulin release. The insulin release elicited by 28 and 50 mM [K+]o was similar in terms of peak, total release and half-time from maximum release. Stepwise increase in [K+]o from 10 to 28 to 50 mM resulted in a normal response to 28 mM but no peak of release after the 28 to 50 mM increase. The results indicate good correlation between excess voltage noise, thought to reflect calcium channel activity, and insulin release evoked by changing extracellular potassium.