DIRECT ELECTRICAL-STIMULATION OF INSULIN-SECRETION BY INTACT MURINE ISLETS OF LANGERHANS THROUGH THE CULTURE SUPPORT

We investigated electrical stimulation of insulin release from intact murine islets, using a noninjurious electrochemical method. The cumula tive insulin concentration in the medium was determined by radioimmuno assay (RIA). Islets were cultured on a transparent conductive film of fluorine-doped tin oxide, under potentiostatic conditions, using an el ectrochemical method based on impedance measurements. The influence of a sine-wave modulation superimposed on the DC resting potential of th e working electrode (+215 mV/SCE) was investigated as a function of ti me at two frequencies (1 and 15 Hz) at a constant amplitude (50 mV). T he influence of a DC potential (-700 and +600 mV/SCE) without modulati on was also studied, especially with regard to the sign of the corresp onding charge on the support. Both frequency and DC potential have a m arked effect on islet behavior, according to the stimulation duration, as shown by the insulin concentration after stimulation. According to the values of the parameters, insulin release was enhanced (15 Hz or -700 mV after stimulation for 24 h) or inhibited (1 Hz and +600 mV). T he stimulation was ascertained to be reversible, since the morphology of islets remained normal and their hormonal function was unaltered. T his effect of long-term electrical stimulation was interpreted by post ulating the existence of a micronervous system at the level of the isl et.