Microelectrode studies of D-glucose- and K⁺-induced changes in membrane potential of electrofused insulin-producing cells

In the present study electrical field-induced fusion has been applied to both normal pancreatic islet cells isolated from obese hyperglycemie mice and clonal insulin-producing cells (RINmSF) derived from a transplantable rat insulinoma. The fused cells were then punctured with microelectrodes to measure changes in membrane potential after exposure to stimulatory concentrations of D-glucose or K⁺. Fused cells of normal islet cellular origin revealed a resting membrane potential of -60 mV and were depolarized by 24 or 27 mV after exposure to 11 mM D-glucose or 30 mM K⁺. Although D-glucose induced depolarization, it was not possible to establish the existence of an oscillating burst pattern superimposed by action potentials. The resting membrane potential of the fused RINm5F cells was also -60 mV and decreased to -30 mV after exposure to 30 mM K⁺. As judged from the membrane potential measurements, the reconstitution of the plasma membrane subsequent to electrical breakdown is essentially the same whether the giant cells originated from normal islet cells or RINm5F cells.