Electrical responses of smooth muscle cells of the mouse uterus to adenosine triphosphate.

Abstract

SUMMARY1. Electrical responses of the smooth muscle cells to ATP were recorded in the longitudinal muscle of mouse myometrium, using intracellular micro-electrodes.2. ATP (> 10-7 M) dose-dependently produced a biphasic change in the membrane potential, an initial hyperpolarization (20-30 see) and then a depolarization. This effect of ATP was observed in all stages of gestation. The initial hyperpolarization was more quickly desensitized than the depolarization.3. Application of ATP for a short period (10 see) produced only the initial hyperpolarization; the amplitude was dose-dependently increased.4. During the ATP-induced hyperpolarization and the depolarization, generation of spike potentials was suppressed and enhanced, respectively. Strong outward current restored the spike generation during hyperpolarization.5. During the ATP-induced hyperpolarization, the membrane resistance was decreased. The amplitude of the hyperpolarization was increased in low [K]o solution and decreased in high [K]o solutions.6. Pre-treatment with TEA (1 mM), procaine (1 mM), 4-aminopyridine (0 5 mM) or apamin (2 x 10-7 M) did not, but TEA (5-10 mM) did suppress the ATP-induced hyperpolarization. Involvement of endogenous catecholamines, cyclic AMP, prostaglandins or acetylcholine in the ATP responses was ruled out.7. During the ATP-induced depolarization, the membrane resistance was reduced. In low [Na]0 solutions, the muscle membrane was depolarized and the amplitude of ATP-induced depolarization was reduced. In sodium-free solution, ATP produced only the initial hyperpolarization.8. It was concluded that the electrical responses ofthe smooth muscle cells of mouse myometrium to ATP consist of two components: an initial hyperpolarization with increase in the potassium conductance and a depolarization with increase in the sodium conductance.

Functional expression of purinergic P2X7 receptors in pregnant rat myometrium

“…These channels were permeable to many monovalent cations. ATP was also observed to induce an initial hyperpolarization and depolarization to regulate myometrial cell contraction (25). Recently, some P2 receptor agonists were reported to mediate uterine contractions showing that P2 receptors were present in the myometrium (38).…”

The mechanical response of rat myometrium to adenosine triphosphate in Ca-free solution.

“…It is noteworthy that oxytocin-induced contraction in the absence of external Ca was depressed when a small amount of external Ca was given (Ca reversal;SAKAI and UCHIDA, 1980). Adenosine triphosphate (ATP) is known to induce excitation of membrane activity in pregnant mouse myometrium (NINOMIYA and SUZUKi, 1983). In the present experiment, it was found that a contraction was generated by ATP in the depolarized longitudinal muscle of rat myometrium in the absense of external Ca.…”

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).…”