Transfected cyclic nucleotide-gated channels as biosensors

Differential effects of cGMP produced by soluble and particulate guanylyl cyclase on mouse ventricular myocytes

Particulate guanylyl cyclase (pGC) and soluble guanylyl cyclase (sGC) are cGMP-generation systems distributed in different intracellular locations. Our aim was to test the hypothesis that the functional effects of cGMP produced by pGC and sGC on contraction and Ca2+ transients would differ in ventricular myocytes. We measured myocyte shortening from adult mice using a video edge-detector and investigated the functional changes after stimulating pGC with C-type natriuretic peptide (CNP; 10(-8) M and 10(-7) M) or sGC with S-nitroso-N-acetyl-penicillamine (SNAP; nitric oxide donor; 10(-6) M and 10(-5) M). Significant concentration-dependent decreases in percentage shortening (PCS), maximal rate of shortening (RSmax), and relaxation (RRmax) were produced by CNP. To a similar degree, SNAP concentration-dependently reduced PCS, RSmax, and RRmax. The addition of Rp-8-[(4-chlorophenyl)thio]-cGMPS triethylamine (cGMP-dependent protein kinase inhibitor; 5 x 10(-6) M) or erythro-9-(2-hydroxy-3-nonyl) adenine (cGMP-stimulated cAMP phosphodiesterase inhibitor; 10(-5) M) reduced the responses induced by CNP or SNAP, suggesting that their actions were through cGMP-mediated pathways. While SNAP significantly increased intracellular cGMP concentration by 57%, CNP had little effect on cGMP production. We also found that CNP markedly decreased the amplitude of Ca2+ transients while SNAP had little effect, suggesting the cGMP generated by sGC may decrease myofilament Ca2+ sensitivity. The small amount of cGMP generated by pGC had a major effect in reducing Ca2+ level. This study suggested the existence of compartmentalization for cGMP in ventricular myocytes.