The mechanical response of the isolated longitudinal muscle of pregnant rat myometrium to adenosine triphosphate in the Ca-free solution containing various polyvalent cations.

Abstract

A small tonic contraction could be evoked by 3 mM adenosine triphosphate (ATP) in the longitudinal muscle of pregnant rat myometrium which was incubated with the Ca-, Mg-free solution containing 2 mM EGTA (40 mM K). The amplitude of the tonic contraction was decreased by exposure to the solution within a few hours, but was again increased when 1-10 mM Mg was added to the Ca-free solution. The ATP-induced contraction was increased for more than 7 h during exposure to the Cafree solution containing Mg ions. The ATP-induced contraction in the Cafree (Mg-free) solution was also produced when the solution contained 1 mM Mn or 1.5 mM La. On the other hand, the tonic contraction evoked by 1 mM Ca or Ba in the presence of 40 mM K was depressed by ATP. The above results led us to propose that the ATP-induced contraction evoked in the Ca-free solution containing Mg was mediated by a process independent of Ca, and possibly mediated by a translocation of Mg in the cell. La and Mn could take the place of Mg in producing a tonic contraction caused by ATP application.

Changes in expression of P2X1 receptors and connexin 43 in the rat myometrium during pregnancy

“…Adenosine 5 0 -triphosphate causes direct contraction of rodent myometrial smooth muscle cells in the nonpregnant (40)(41)(42)(43) and pregnant myometrium (44,45), probably acting via P2X 1 receptors. In the human pregnant uterus, contractions caused by P2X 1 receptor stimulation increased with the progression of pregnancy (46), consistent with this study, in which expression of P2X 1 receptors increased during pregnancy.…”

Effects of cytochalasins on the mechanical and membrane responses in the isolated longitudinal myometrium of pregnant rat with reference to the EGTA-resistant contraction.

“…Effects of cytochalasins on the contractile and membrane activities It was shown in a previous report that ATP induced a maintained contraction in the longitudinal myometrium of pregnant rat which was exposed to Ca-free solution (OsA and MARUTA, 1987b). It was attempted in the experiment shown in Fig.…”

“…1, 2). AA dependence of such Ca-free contraction on Mg-influx was recently proposed for the canine gastric muscle (FILIPPONI et al, 1987) and rat myometrium (OsA and MARUTA, 1987b). According to the nomenclature of FILIPPONI et al .…”

Purinergic Signalling in the Reproductive System

“…In freshly isolated myometrial cells from pregnant rats treatment with ATP induces contractions and P2X 7 receptor-mediated currents, and the effect can be blocked with Mg 2+ (Urabe et al, 2009;Miyoshi et al, 2010Miyoshi et al, , 2012. Depending on the species and hormonal phase/pregnancy, myometrial contractions can be induced with ATP, UTP or ADP (Urabe et al, 2009;Bülbring et al, 1968;Dozi-Vassiliades et al, 1976;Ninomiya and Suzuki, 1983;Osa and Maruta, 1987;Ziganshin et al, 2006), and they involve the action of prostaglandins (Moritoki et al, 1979;Suzuki, 1991;Aitken et al, 2001). Whole cell voltage clamp studies in primary cultures of pregnant rat myometrial cells showed that ATP activated a monovalent cation-selective and estrogen-sensitive conductance (Honoré et al, 1989).…”