Voltage-dependent stimulation of the Na+-K+ pump by insulin in rabbit cardiac myocytes

Insulin enhances Na+-K+ pump activity in various noncardiac tissues. We examined whether insulin exposure in vitro regulates Na+-K+ pump function in rabbit ventricular myocytes. Pump current (I-p) was measured using the whole-cell patch-clamp technique at test potentials (V(m)s) from -100 to +60 mV. When the Na+ concentration in the patch pipette ([Na](pip)) was 10 mM, insulin caused a V-m-dependent increase in I-p. The increase was similar to 70% when V-m was at near physiological diastolic potentials. This effect persisted after elimination of extracellular voltage-dependent steps and when K+ and K+-congeners were excluded from the patch pipettes. When [Na](pip) was 80 mM, causing near-maximal pump stimulation, insulin had no effect, suggesting that it did not cause an increase in membrane pump density. Effects of tyrphostin A25, wortmannin, okadaic acid, or bisindolylmaleimide I in pipette solutions suggested that the insulin-induced increase in I-p involved activation of tyrosine kinase, phosphatidylinositol 3-kinase, and protein phosphatase 1, whereas protein phosphatase 2A and protein kinase C were not involved.