Studies on ATP receptor and K ATP channel to regulate uterine contractility for tocolysis

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ATP has been reported to enhance the membrane conductance of myometrial cells and uterine contractions. Some types of ATP (P2X and P2Y) receptor were detected in myometrium using molecular biological methods. However, the role of ATP receptor in regulating uterine contractions is not well understood. ATP receptor currents were recorded from single rat myometrial cells using the whole cell patch clamp method.ATP receptor currents were activated with extracellular ATP in the range of 10,М-1mM.. These currents were in rectangular shapes and should induce membrane depolarizations (pacemaker potentials). ATP receptor had permeability to various monovalent ions and the order of conductance was K^+>Cs^+>Li^+>Na^+. ATP receptor was activated by ADP, GTP, UTP, 2-methylthio ATP and,-methylene ATP by 13 %, 40 %,44 %, 85 %n, and 108 % comparing with ATP of 0.1mM. These currents were blocked by suramin (blocker of P2 receptor) and PPADS (blocker of P2X receptor), indicating P2X receptor is the main component in myometrial cells. Extracellular Mg^<2+> inhibited ATP receptor currents in a dose-dependent manner and the Kd was calculated to be 0.26mM.P2X is the dominant component of ATP receptor in myometrial cells and the currents are thought to induce pacemaker potentials leading to rhythmical uterine contraction in labor. Blocking of ATP receptor may be one of the mechanisms for the inhibition of uterine contractions in tocolysis as reported in studies on myometrial non-selective cation channel.