The membrane potential of L6 muscle cells was measured with the fluorescent dye bis-oxonol. Hyperpolarizations of up to 15 mV were caused by gramicidin (in N-methyl-D-glucamine+ medium), or by monensin or ionomycin. Depolarization was achieved with gramicidin (in Na+ medium), or with K+. Insulin did not change the resting membrane potential of − 70 mV, yet it effectively stimulated 2-deoxy-D-glucose uptake. Conditions that hyperpolarize the cells did not alter the basal rate of hexose uptake. Moreover, insulin was still capable of stimulating hexose uptake in depolarized cells. It is concluded that modulation of the membrane potential is probably not a signalling event in insulin stimulaton of hexose uptake.
