Islet electrical pacemaker response to alpha-adrenergic stimulation

Abstract

To characterize the pancreatic islet cell responses to adrenergic stimulation, membrane potentials have been recorded from isolated, perifused mouse islets of Langerhans exposed to a steady glucose level of 200 mg/dl. Various doses of epinephrine HCl from 5 to 10,000 nM have been applied for 10--15-min test periods separated by 10--15-min control periods. Epinephrine produced a dose-dependent suppression of glucose-induced membrane electrical activity. Adding epinephrine (50--100 nM) reduced the plateau fraction (the fraction of each plateau/silent phase cycle spent in the plateau phase) from 0.41 +/- 0.03 (X +/- SEM, N = 13) to 0.28 +/- 0.08 (N = 5, P = 0.05) and more markedly reduced the plateau frequency from 2.56 +/- 0.32 (N = 13) to 0.80 +/- 0.23 min-1 (N = 5, P less than 0.02). Adding 10- and 100-fold higher concentrations of epinephrine had little additional effect. There was no effect of epinephrine on the membrane potential levels of the plateau and silent phase after a new steady state was achieved and no effect on the amplitude and waveform of the rapid spikes. The pattern of inhibition of the plateau/silent phase cycles by epinephrine is qualitatively different from the pattern seen during inhibition of electrical activity by reducing glucose level. This suggests that the electrical rhythm is controlled by more than one pathway. The persistence of electrical activity at very high levels of epinephrine (to 10,000 nM) suggests that electrical activity and, therefore, Ca2+ uptake can exist in the absence of insulin release.