Alterations in ventricular myocyte contraction caused by C-type natriuretic peptide and nitric oxide in eNOS–/– mice

Lack of endothelial nitric oxide synthase (eNOS) may affect the sensitivity of cyclic GMP signaling through soluble guanylyl cyclase (sGC). We hypothesized that in eNOS knockout (eNOS–/–) mice, stimulation of guanylyl cyclase would have enhanced effects inhibiting cardiac contraction. We measured cell shortening and calcium transients in isolated ventricular myocytes from adult eNOS–/– and wild-type (WT) mice after stimulating particulate guanylyl cyclase (pGC) with C-type natriuretic peptide (CNP, 10–8 and 10–7 M) or sGC with S-nitroso-N-acetyl-penicillamine (SNAP, NO donor, 10–6 and 10–5 M). Although sGC activity was increased by +71% in eNOS–/–, SNAP had similar effects in the two groups (%shortening –39% control vs. –37% eNOS–/–), suggesting that the cyclic GMP pathway was desensitized in eNOS–/– myocytes. CNP had significantly smaller effects on cell contraction (%shortening –34% control vs. –14% eNOS–/–) and pGC activity was not changed in eNOS–/– myocytes. Similar effects were also produced by guanylin and carbon monoxide, stimulators of pGC and sGC. CNPʹs effects on Ca2+ transients were also attenuated in eNOS–/– myocytes. SNAP did not alter Ca2+ transients in eNOS–/– or control cells. In the eNOS–/– mice, cyclic GMP-dependent protein kinase and cyclic AMP phosphodiesterase activity were reduced. This study demonstrated that the downstream cyclic GMP pathway was attenuated in eNOS–/– mice and this was partially compensated for by increased sGC, but not pGC activity in ventricular myocytes.