Molecular studies on P2 and TRP channels to regulate uterine contractions

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Two types of non-selective cation channel (NSCC) currents have been identified in rat myometrial cells using. These channels are thought to regulate uterine contractions during labor and to be a target of magnesium sulfate for tocolysis. The purpose of this study was to determine the channel subtypes of NSCC with molecular methods and reconstruct to characterize the dominant channels in a cultured cell line.The expression of P2X and TRP (subtype C) channels was studied by RT-PCR in rat myometrium from pregnant rats at days 19. The cloned DNA of P2X4 was transfected into the cultured COS-7 cell line. The whole cell patch clamp method was applied to characterize the expression of the myometrial P2X4 channels.The expression of mRNA was checked for each subtype of TRP and P2X channels. TRPC1,3,4 and 6 were identified in myometrium. TRPC3 was dominantly expressed and the sequence was determined. The homology was higher than 97% compared with rat heart and brain. All subtypes, X1 through X7 of P2X were detected in rat myometrium. P2X4 was the dominant subtype. The sequence of P2X4 was determined and the homology was higher than 99%. The expressed channels in COS-7 cells were induced by external application of ATP and most of the properties were similar to P2X channels in native myometrial cells. However, the desensitization to ATP was observed to be faster than that of native P2X channels.The mRNA expression of TRP and P2X channels has been detected in pregnant rat myometrium. TRPC3 and P2X4 are thought be the main channels of myometrial NSCCs. TRPC3 has been reported to be the dominant subtype in human myometrial cells for the intracellular calcium storage. Our results suggest both TRPC3 and P2X4 may induce depolarization of the cell membrane leading to uterine contractions.