Tension elicited by depolarizing pulses in pregnant rat uterine muscle consists of a slow inward current-dependent component and a second component suggesting calcium release from intracellular stores.
In pregnant rat uterine smooth muscle, contraction involves both a slow inward calcium current and the release of calcium from intracellular stores.
The relationship between ionic currents and contraction has been investigated in uterine strips of pregnant rat by means of a double sucrose gap apparatus combined with an optical method which permits the measurement of the contraction of the small muscular bundle where potential and current are recorded.2. Effects of duration, size and frequency of imposed potentials upon contraction have been studied. The uterine muscle shows summation and tetanus phenomena. Tension elicited by depolarizing pulses of different durations and amplitudes can be considered as made of two components.3. The first component of the contraction evoked by short depolarizing steps (about 50 ms) depends on the slow inward current. This contraction is abolished by manganese and lanthanum ions and by compound D 600. The amplitude of the tension can be related to the external calcium concentration and consequently to the calcium influx. The slow inward current is supposed to release a part of the bound calcium without excluding, however, a direct activation of myofibrils.4. The second component of the contraction is observed in manganese containing solution with depolarizations longer than 200 ms and without inward current. Such a component of tension suggests the possibility of release of calcium from intracellular stores which could be located in the sarcoplasmic membrane of the uterine smooth muscle.
Jean Mironneau (Wed,) conducted a other in Pregnant rat uterine smooth muscle. Depolarizing pulses and ion channel blockers (manganese, lanthanum, compound D 600) was evaluated on Contraction/tension and ionic currents. Tension elicited by depolarizing pulses in pregnant rat uterine muscle consists of a slow inward current-dependent component and a second component suggesting calcium release from intracellular stores.