| Abstract: | The published data on the mechanisms and regulation of active and passive Ca2+ transport in the myometrium have been analyzed. Particular attention is paid to the cGMP-dependent and independent pathways of action of nitric oxide or its derivatives on intracellular Ca2+ homeostasis of uterine smooth muscle and its contractile activity. Information on the effect of nitric oxide on Ca2+ -transport systems of other types of smooth muscles is provided in a comparative aspect. Based on own experimental results and literature data a scheme of NO action in the myometrium is suggested in which nitric oxide or its derivatives cause Ca2+ -dependent polarization of the sarcolemma. In accordance with our results, this effect may be based on the increase of sarcolemma Ca2+ permeability under the influence of NO or its derivatives and the stimulation of at least the initial passive transport of the cation in the myocytes mediated by dihydropyridine-sensitive channels. Additional factors that contribute to the polarization of the membrane are the increase of protons transport from the muscle cells and stimulation of Na+, K+ -ATPase. Acting on the sarcoplasmic reticulum, nitrosactive compounds activate the inclusion of calcium in this compartment and inhibit Ca2+ -induced release of the cation. The latter effects are able to provide compensation for NO-induced Ca2+ increase in myocytes and supress the electromechanical coupling at Ca2+ release from the reticulum. NO-derivates also inhibit a key link in the smooth muscle contractile act--the formation of the Ca2+ -calmodulin complex. |
