ABSTRACT
This chapter focuses on the different ion channels present in myometrial cells and how they can modulate the contractile activity of the uterus during pregnancy. Calcium can enter the cell through plasma membrane channels of two different classes. In the simplest model, calcium channels are in one of three configurations: closed, open, or inactivated. Calcium channel current density, normalized by cell capacitance, significantly increases during gestation. Changes in sodium channel density have been studied during gestation. The insertion of fast sodium channels into the cell membrane may cause an elevation of intracellular calcium concentration by the sodium-calcium exchange system functioning in the reverse mode, which can, in turn, potentiate the myometrial contraction. Chloride channels, activated by both release of calcium from the intracellular store and calcium influx through voltage-dependent calcium channels, have been identified in visceral and vascular smooth muscles.
