Effects of magnesium and temperature during the recovery process from the potassium contracture of the pregnant rat myometrium.
Effects of external ions (Na, K, Mg) on the recovery from K-contracture of the pregnant rat myometrium were investigated in Ca-free media. Relaxation was faster, when the external concentration of Na and K ions was higher. The time course of relaxation within a limited range of 60-20% of the mechanical output followed a single exponential function. The rate of relaxation, given by the reciprocal of the period during which the contraction decayed to 1/e, was 0.3-0.5 min-1 at 34-35 degrees C in isotonic Na solution. Low temperature caused prolongation of the relaxation, and the activation energy estimated on the rate of relaxation was 3-4 kcal-mol-1. Relaxation became faster when Mg (0.5-20 mM) was added to the relaxation media. Relaxation in isotonic K media was slower than in isotonic Na media, and the addition of Mg caused a slight acceleration of the relaxation. Low temperature caused an acceleration of the relaxation, irrespective of the presence or absence of external Mg ions. In low K media, where K ions were replaced by isomolar sucrose, addition of Mg caused a significant acceleration of the relaxation. Activation energy ranged between 13-15 kcal mol-1 in the solutions containing Mg. This favors the existence of a relaxing system in pregnant rat myometrium that is Mg- and metabolism-linked.
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D007477:Ions; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009215:Myometrium / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011247:Pregnancy; D011270:Pregnancy, Animal; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013696:Temperature; D014599:Uterus / Q000187:drug effects*
D007477:Ions; D011189:Potassium Chloride; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium