Opposing effects of coupled and uncoupled NOS activity on the Na + -K + pump in cardiac myocytes

Pharmacological delivery of nitric oxide (NO) stimulates the cardiac Na+-K+ pump. However, effects of NO synthesized by NO synthase (NOS) often differ from the effects of NO delivered pharmacologically. In addition, NOS can become “uncoupled” and preferentially synthesize O2·−, which often has opposing effects to NO. We tested the hypothesis that NOS-synthesized NO stimulates Na+-K+ pump activity, and uncoupling of NOS inhibits it. To image NO, we loaded isolated rabbit cardiac myocytes with 4,5-diaminofluorescein-2 diacetate (DAF-2 DA) and measured fluorescence with confocal microscopy. l-Arginine (l-Arg; 500 μmol/l) increased DAF-2 DA fluorescence by 51% compared with control (n = 8; P < 0.05). We used the whole cell patch-clamp technique to measure electrogenic Na+-K+ pump current (Ip). Mean Ip of 0.35 ± 0.03 pA/pF (n = 44) was increased to 0.48 ± 0.03 pA/pF (n = 7, P < 0.05) by 10 μmol/l l-Arg in pipette solutions. This increase was abolished by NOS inhibition with radicicol or by NO-activated guanyly...