The nitric oxide donor sodium nitroprusside stimulates the Na+-K+ pump in isolated rabbit cardiac myocytes.
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 (I(p)) in rabbit ventricular myocytes. Myocytes were voltage clamped with wide-tipped patch pipettes to achieve optimal perfusion of the intracellular compartment, and I(p) was identified as the shift in holding current induced by 100 microm ouabain. The NO donor sodium nitroprusside (SNP) in concentrations of 1, 10, 50 or 100 microm induced a significant increase in I(p) 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 YC-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(+).
William
Maged
M
Department of Cardiology, Royal North Shore Hospital, St Leonards, NSW 2065, Australia.
Vien
Jimmy
J
Hamilton
Elisha
E
Garcia
Alvaro
A
Bundgaard
Henning
H
Clarke
Ronald J
RJ
Rasmussen
Helge H
HH
D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D020536:Enzyme Activators / Q000494:pharmacology; D006162:Guanylate Cyclase; D066298:In Vitro Techniques; D007191:Indazoles / Q000494:pharmacology; D008297:Male; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000201:enzymology*; D020030:Nitric Oxide Donors / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D011817:Rabbits; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D015290:Second Messenger Systems / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D000071756:Soluble Guanylyl Cyclase
D020536:Enzyme Activators; D007191:Indazoles; D020030:Nitric Oxide Donors; D018160:Receptors, Cytoplasmic and Nuclear; C090937:3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole; D009599:Nitroprusside; D012964:Sodium; D006162:Guanylate Cyclase; D000071756:Soluble Guanylyl Cyclase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium