The nitric oxide donor sodium nitroprusside stimulates the Na+-K+ pump in isolated rabbit cardiac myocytes

Abstract

Nitric oxide (NO) affects the membrane Na+-K+ pump in a tissue-dependent manner. Stimulation of intrinsic pump activity, stimulation secondary to NO-induced Na+ influx into cells or inhibition has been reported. We used the whole-cell patch clamp technique to measure electrogenic Na+-K+ pump current (Ip) in rabbit ventricular myocytes. Myocytes were voltage damped with wide-tipped patch pipettes to achieve optimal perfusion of the intra-cellular compartment, and Ip was identified as the shift in holding current induced by 100 μM ouabain. The NO donor sodium nitroprusside (SNP) in concentrations of 1, 10, 50 or 100 μM induced a significant increase in IP when the intracellular compartment was perfused with pipette solutions containing 10 mM Na+, a concentration near physiological levels. SNP had no effect when the pump was near-maximally activated by 80 mm Na+ in pipette solutions. Stimulation persisted in the absence of extracellular Na+, indicating its independence of transmembrane Na+ influx. The SNP-induced pump stimulation was abolished by inhibition of soluble guanylyl cyclase (sGC) with 1H-[1,2,4] oxadiazole [4,3-a]quinoxalin-1-one, by inhibition of protein kinase G (PKG) with KT-5823 or by inhibition of protein phosphatase with okadaic acid. Inclusion of the non-hydrolysable cGMP analogue 8pCPT-cGMP, activated recombinant PKG or the sGC-activator YG-1 in patch pipette filling solutions reproduced the SNP-induced pump stimulation. Pump stimulation induced by YC-1 was dependent on the Na+ concentration but not the K+ concentration in pipette filling solutions, suggesting an altered sensitivity of the Na+-K+ pump to intracellular Na+. © The Physiological Society 2005.