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 cumulative insulin concentration in the medium was determined by radioimmunoassay (RIA). Islets were cultured on a transparent conductive film of fluorine-doped tin oxide, under potentiostatic conditions, using an electrochemical method based on impedance measurements. The influence of a sine-wave modulation superimposed on the DC resting potential of the working electrode (+215 mV/SCE) was investigated as a function of time at two frequencies (1 and 15 Hz) at a constant amplitude (50 mV). The influence of a DC potential (-700 and +600 mV/SCE) without modulation was also studied, especially with regard to the sign of the corresponding charge on the support. Both frequency and DC potential have a marked 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). The stimulation was ascertained to be reversible, since the morphology of islets remained normal and their hormonal function was unaltered. This effect of long-term electrical stimulation was interpreted by postulating the existence of a micronervous system at the level of the islet.