Signalling mechanisms in contraction‐mediated stimulation of intracellular NO production in cat ventricular myocytes

In this study we sought to determine whether contractile activity has a role as a signalling mechanism in the activation of intracellular nitric oxide (NO i ) production induced by electrical stimulation of cat ventricular myocytes. Field stimulation (FS) of single ventricular myocytes elicited frequency‐dependent increases in NO i that were blocked by the calmodulin (CaM) inhibitor 10 μ m W‐7 and partially inhibited by the phosphatidylinositol 3′‐kinase (PI‐(3)K) inhibitor 10 μ m LY294002. Increasing extracellular [Ca 2+ ] caused a concentration‐dependent increase in FS‐induced NO i that was partially inhibited by LY294002. The negative inotropic agents BDM (5 m m ) or blebbistatin (10 μ m ) decreased cell shortening and NO i production without concomitant changes in L‐type Ca 2+ current ( I Ca,L ) or [Ca 2+ ] i transients. The positive inotropic agents EMD 57033 or CGP 48506 (1 μ m ) increased cell shortening and NO i production without concomitant changes in I Ca,L or [Ca 2+ ] i transients. FS‐induced NO i production was decreased in myocytes infected (100 multiplicity of viral infection (MOI); 24 h) with a replication‐deficient adenovirus expressing a dominant‐negative mutant of protein kinase B (Akt) compared with cells infected with a control adenovirus expressing β‐galactosidase. FS‐induced NO i was partially inhibited by either endothelial (eNOS) or neuronal nitric oxide synthase (nNOS) inhibitors and completely blocked by simultaneous exposure to both. FS‐induced [Ca 2+ ] i transients were increased by the nNOS inhibitor nNOS‐I (0.24 μ m) , decreased by the eNOS inhibitor L‐NIO (1 μ m ) and unchanged by exposure to both inhibitors. We conclude that in cat ventricular myocytes, FS‐induced NO i production requires both Ca 2+ ‐dependent CaM signalling and Ca 2+ ‐independent PI‐(3)K–Akt signalling activated by contractile activity. FS activates NO i production from both eNOS and nNOS, and each source of NO i exerts opposing effects on [Ca 2+ ] i transient amplitude. These findings are important for understanding the regulation of NO i signalling in the normal and mechanically failing heart.