Glucose- and concentration-dependence of noradrenalin effects on electrical activity in mouse pancreatic beta cells

The effects of a wide range of noradrenalin (NA) concentrations (10(-11)-10(-4) M) on the membrane potential and on the glucose-induced electrical activity were investigated with microelectrodes in microdissected mouse islets. In the presence of 11.1 mM glucose, the beta cells exhibited a repetitive activity. NA at more than 10(-7) M induced a rapid hyperpolarization followed by a silent depolarization, then by the appearance of a slowed pace of repetitive activity (dose-dependent effects). NA at less than 10(-7) M did not markedly affect the electrical activity; it only induced a dose-dependent increase in the degree of activity with no change of the potential levels. The glucose-dependence of these effects were then investigated. In the absence of glucose, 10(-8) and 10(-6) M NA did not affect the resting membrane potential. Non-stimulatory glucose concentrations (2.8-7.3 mM) progressively decreased the membrane potential. 10(-8) M NA did not affect it, while 10(-6) M NA induced a dose-dependent and long-lasting hyperpolarization. In the presence of stimulatory glucose concentrations (7.3-30 mM) the degree of activity increased, 10(-8) M NA induced a slight leftward shift and 10(-6) M NA a slight rightward shift of the dose-response curve.