Does cGMP Have Other Effects on Mechanisms Important for Synchronization?
In tracheal VSMC, it has previously been suggested that cGMP reduces release of Ca2+ from the SR. If this also occurs in the arteries, it could potentially be of importance for vasomotion. To test this possibility, cGMP concentration response curves at a constant noradrenaline concentration were made under conditions where the membrane was kept hyperpolarized with pinacidil. Our finding that the cGMP concentration-dependent reduction of the number of cells producing waves and the frequency of Ca2+ waves within the individual VSMC strongly suggest that cGMP reduces the probability of Ca2+ release from the SR. This observation is consistent with the finding in isolated tracheal VSMC, where 100 µM 8Br-cGMP reduced the frequency of acetylcholine-induced, SR-dependent [Ca2+] i transients [20]. This effect of cGMP might either occur through stimulation of Ca2+ extrusion from the cells via stimulation of the plasma membrane Ca-ATPase [21], via stimulation of Na-Ca exchange [22] or perhaps thr
