Hyperpolarization as a mediator of insulin action: increased muscle glucose uptake induced electrically

Insulin hyperpolarizes. This raises the questions: is hyperpolarization a means by which insulin exerts some of its other effects, and can electrically induced hyperpolarization mimic insulin action on membrane functions? A technique was devised to study the latter question. The technique permits electrical hyperpolarization of a segment of whole muscle. Rat caudofemoralis muscle was threaded into a triple sucrose-gap chamber. Continuous flow of sucrose displaced interstitial fluid of muscle segments in the gaps. In one electrolyte compartment between gaps was placed an anode and in the other a cathode. The muscle segment in the anodal compartment was hyperpolarized continuously for 30 min, probably by about 1.5 mV. Uptake of deoxyglucose was increased in the hyperpolarized muscle segment. This increase, by 39%, was highly significant. It was probably smaller than the twofold increase elicited by insulin (100 mU/ml), but not than the possible effect produced by 10 mU/ml. The effect of hyperpolarization was specific for the D-glucose transport system because uptake of L-glucose was not altered.