The relation between membrane potential, membrane currents and activation of contraction in ventricular myocardial fibres

摘要: 1. Membrane currents and contractile responses have been measured in ventricular myocardial preparations under voltage clamp conditions. 2. In Tyrode solution, steady-state contraction was obtained only after 5-8 depolarizations to a given potential level. The threshold of tension identical the where calcium inward current, ICa, activated (about −35 mV). Both thresholds were shifted same direction along axis by amount changing [Ca]o or [Na]o. Maximum at inside positive potentials. 3. time courses activation ICa different more than one order magnitude solution. But achieve any appreciable tension, had flow during several depolarizations. Tension decreased again potentials above ECa. This suggests that current must fill intracellular stores from which can be released an unknown mechanism. 4. ability fibre bundle contract preceding twitch is greatly dependent on membrane between two equal solutions with 1·8 7·2 m M-CaCl2 half restoration this occurred −45 ± 3 mV (± S.E. mean) −23 4 mV, respectively. 5. sodium-free bathing solutions, attained upon first depolarization provided activated. Furthermore, potentials, identical, i.e. reached its maximum when fully ions into directly activates contraction.