Mechanisms of Na+-K+ pump regulation in cardiac myocytes during hyposmolar swelling.
We have previously demonstrated that the sarcolemmal Na+-K+ pump current (Ip) in cardiac myocytes is stimulated by cell swelling induced by exposure to hyposmolar solutions. However, the underlying mechanism has not been examined. Because cell swelling activates stretch-sensitive ion channels and intracellular messenger pathways, we examined their role in mediating Ip stimulation during exposure of rabbit ventricular myocytes to a hyposmolar solution. Ip was measured by the whole cell patch-clamp technique. Swelling-induced pump stimulation altered the voltage dependence of Ip. Pump stimulation persisted in the absence of extracellular Na+ and under conditions designed to minimize changes in intracellular Ca2+, excluding an indirect influence on Ip mediated via fluxes through stretch-activated channels. Pump stimulation was protein kinase C independent. The tyrosine kinase inhibitor tyrphostin A25, the phosphatidylinositol 3-kinase inhibitor LY-294002, and the protein phosphatase-1 and -2A inhibitor okadaic acid abolished Ip stimulation. Our findings suggest that swelling-induced pump stimulation involves the activation of tyrosine kinase, phosphatidylinositol 3-kinase, and a serine/threonine protein phosphatase. Activation of this messenger cascade may cause activation by the dephosphorylation of pump units.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D048429:Cell Size; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006706:Homeostasis; D007038:Hypotonic Solutions; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009025:Morpholines / Q000494:pharmacology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism; D054645:Protein Phosphatase 1; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D020032:Tyrphostins / Q000494:pharmacology