Effects of calcium channel blocker, mibefradil, and potassium channel opener, pinacidil, on the contractile response of mid-pregnant goat myometrium.

Sep 29, 2005Indian journal of experimental biology

How calcium and potassium channel drugs affect uterine muscle contractions in mid-pregnant goats

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Abstract

Mibefradil and pinacidil inhibited spontaneous rhythmic contractions of isolated goat uterine strips at concentrations of 100 μM and 10 μM, respectively.

Both mibefradil and pinacidil caused concentration-dependent inhibition of spontaneous rhythmic contractions.
The rhythmic contractions were abolished at 100 μM for mibefradil and at 10 μM for pinacidil.
Mibefradil at concentrations of 1 and 10 μM antagonized contractions induced by oxytocin.
Pinacidil also antagonized oxytocin-induced contractile responses in a concentration-related manner.
Pretreatment with glibenclamide led to a rightward shift in the concentration-response curve of pinacidil, indicating interaction with KATP channels.

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The present study was undertaken to investigate the in vitro influence of mibefradil, a calcium channel blocker, and pinacidil, a potassium channel opener, on pregnant goat myometrial spontaneous rhythmic contractility and contractions induced with the agonist, oxytocin. Longitudinal strips from the distal region of uterus, collected from goats at midgestation, were mounted in an organ bath for recording isometric contractions. Mibefradil (10(-8)-10(-4) M) or pinacidil (10(-10)-10(-4) M), added cumulatively to the bath at an increment of 1 log unit, caused concentration-dependent inhibition of the spontaneous rhythmic contractions of isolated uterine strips. The rhythmic contraction was, respectively, abolished at 100 and 10 microM concentrations of mibefradil and pinacidil. In a concentration-dependent manner, mibefradil (1 and 10 microM) antagonized the contractions elicited with oxytocin (10(-5)-10(-2) IU). Pretreatment of uterine strips with glibenclamide (10 microM), a selective KATP channel blocker, caused a rightward shift of the concentration-response curve of pinacidil with a concomitant decrease in its pD2 value. Pinacidil (0.3, 1 and 3 microM), in a concentration-related manner, antagonized the oxytocin (10(-5)-10(-2) IU)-induced contractile response. The inhibition of spontaneous rhythmic contractions and antagonism of oxytocin-induced contraction by mibefradil in the pregnant goat myometrium may be related to the antagonism of voltage-dependent Ca2+ channels, while by pinacidil suggests that KATP channel could be a therapeutic target for tocolysis.

Effects of calcium channel blocker, mibefradil, and potassium channel opener, pinacidil, on the contractile response of mid-pregnant goat myometrium.

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