Rises in intracellular calcium are essential for contraction of human myometrial smooth\ud muscle (HMSM) and hence parturition. The T-type calcium channel may play a role in\ud this process. The aim was to investigate the role of the T-Type calcium channel in\ud HMSM by characterizing mRNA expression, protein localization, electrophysiological\ud properties and function of the channel subunits Cav3.1(α1G), Cav3.2(α1H), and\ud Cav3.3(α1I). QRT-PCR, immuno-histochemistry, electrophysiology and invitro\ud contractility were performed on human myometrial samples from term, preterm, labour\ud and not in labour. QRT-PCR analysis of Cav3.1, Cav3.2 and Cav3.3 demonstrated\ud expression of Cav3.1 and Cav3.2 with no significant change (P>0.05) associated with\ud gestation or labour status. Immuno-histochemistry localized Cav3.1 to myometrial and\ud vascular smooth muscle cells whilst Cav3.2 localized to vascular endothelial cells and\ud invading leukocytes. Voltage clamp studies demonstrated a T-type current in 55% of\ud cells. Nickel block of T-type current was voltage sensitive (IC50 of 118.57±68.9 μM at -\ud 30mV). Activation and inactivation curves of ICa currents in cells expressing T-type\ud channels overlapped demonstrating steady state window currents at the resting membrane\ud potential of myometrium at term. Current clamp analysis demonstrated that\ud hyperpolarizing pulses to a membrane potential greater than -80mV elicited rebound\ud calcium spikes that were blocked reversibly by 100μM nickel. Contractility studies\ud demonstrated a reversible decrease in contraction frequency during application of 100μM\ud nickel (P<0.05). We conclude that the primary T-type subunit expressed in some MSMCs\ud is Cav3.1. We found that application of 100 μM nickel to spontaneously contracting\ud human myometrium reversibly slows contraction frequency
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