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

Abstract

4. The ability of a fibre bundle to contract again after a preceding twitch is greatly dependent on the membrane potential between two equal depolarizations. In Tyrode solutions with 1*8 and 7-2 mM-CaCl2 half restoration of this ability occurred at -45 + 3 mV ( + s.E. of mean) and -23 + 4 mV, respectively. 5. In sodium-free bathing solutions, steady-state tension was attained upon the first depolarization provided ICa was activated.

Effects of caffeine and isoprenaline on mammalian ventricular muscle

“…It has been suggested that the inward current fills up partially depleted intracellular stores of calcium which can subsequently be released by an unknown mechanism to activate contraction (Beeler & Reuter, 1970b;Wood, Heppner & Weidmann, 1969). Any increase in the calcium current would therefore increase the concentration of bound intracellular calcium, resulting in an augmented release of calcium on excitation and an increase in the tension developed during contraction.…”

Electrical and Mechanical Responses to Diltiazem in Potassium Depolarized Myocardium of the Guinea Pig

“…It was also suggested that the compound antagonizes calcium ion essential for muscle contraction, thus causing a reduction in the contractile force of the myocardium (1). On the other hand, it has been reported that the slow inward calcium or calcium-sodium current, as well as the fast inward sodium current, is involved in the generation of the action potential of cardiac muscle fibers under normal physiological conditions (4-13).The slow inward calcium current, which is assumed to play an important role in the excitation-contraction coupling in the cardiac muscle (8,12,(14)(15)(16)(17)(18)(19), is disclosed as a result of the inactivation of sodium carrying system when the extracellular concentration of KCI was increased (20)(21)(22)(23) muscle fibers in K-rich solution were also examined. …”

“…The slow inward calcium current, which is assumed to play an important role in the excitation-contraction coupling in the cardiac muscle (8,12,(14)(15)(16)(17)(18)(19), is disclosed as a result of the inactivation of sodium carrying system when the extracellular concentration of KCI was increased (20)(21)(22)(23) muscle fibers in K-rich solution were also examined.…”

Effect of somatostatin on 45Ca fluxes in guinea‐pig isolated atria

“…Furthermore, voltage clamp studies also demonstrated that slow inward Ca current increased as [Ca]. and contractile force were augmented (Beeler & Reuter, 1970;New & Trautwein, 1972). Therefore, the inhibition of 45Ca uptake observed at low and normal [Ca].…”