Participation of BKCa2+ and KATP potassium ion channels in the contractility of human term pregnant myometrium in in vitro conditions.

AIM: The aim of this study was to assess the participation of ligand-sensitive potassium large conductance calcium-activated ion channels (BK(Ca2+) ) and adenosine triphosphate (ATP)-sensitive potassium ion channels (K(ATP) ) using its openers (NS1619 and pinacidil) in the contractility of human term pregnant myometrium in in vitro conditions. METHODS: Human myometrium tissue samples were collected from term pregnant laboring women who had to undergo cesarean section. The contractility of myometrium was induced by the application of oxytocin into the organ bath. Myometrial strips were incubated with the opener of BK(Ca2+) potassium ion channels NS1619 and its antagonist tetraethylammonium or with the opener of K(ATP) potassium ion channels pinacidil and its antagonist glibenclamide. RESULTS: K(ATP) potassium ion channel's opener pinacidil significantly decreased amplitude of myometrial contractions (P < 0.05) as well as frequency of myometrial contractions (P < 0.05) provoked by oxytocin in human term pregnant myometrium in in vitro conditions. The inhibition of the human myometrial contractions of pinacidil was significantly antagonized by its specific antagonist glibenclamide (P < 0.05). BK(Ca2+) potassium ion channel's opener NS1619 did not significantly affect the contractile activity of human term pregnant myometrium induced by the application of oxytocin in in vitro conditions. CONCLUSION: In our experimental study we found that the participation of BK(Ca2+) and K(ATP) potassium ion channels in the contractility of human term pregnant myometrium in labor is probably different.

Utero-relaxant effect of PDE4-selective inhibitor alone and in simultaneous administration with beta2-mimetic on oxytocin-induced contractions in pregnant myometrium.

BACKGROUND: The objective of the study was to observe the effect of rolipram, the prototype phosphodiesterase 4 selective inhibitor, on oxytocin-induced contractions of human term myometrial strips, and compare the effect with salbutamol, beta(2)-adrenergic agonist, in single and the simultaneous application. METHODS: Human myometrium was obtained from pregnant women in term that had a term delivery by the caesarian section. Myometrial strips were excised from the lower uterine segment and placed into an organ-bath with Krebs-Henseleit buffer. The mean peak amplitude of contraction (mN) of the myometrial smooth muscle to the doses of oxytocin (10(-6) mmol/L(-1)) with subsequent single administration of rolipram (10(-4) mmol/L(-1)), salbutamol (10(-4) mmol/L(1)) and simultaneous administration of rolipram and salbutamol (both 10(-4) mmol/L(-1)), was used as a parameter of myometrial reactivity. RESULTS: Rolipram alone decreased the oxytocin-induced contractile amplitude to 47.98%, single salbutamol application resulted in amplitudinal decrease to 56.07%, and the combination of both compounds in their simultaneous administration resulted in the decrease of oxytocin-induced contractile amplitude to 29.1%. CONCLUSION: Our data are consistent with previous studies of the enhanced efficiency of the beta(2)-adrenergic agonist, when administered together with the phosphodiesterase 4-inhibitor. Moreover we have shown that rolipram alone has a more profound effect on oxytocin-induced contractions than salbutamol alone.