Abstract
The dependence of the rate of calcium efflux from cardiac sarcoplasmic reticulum on the concentration of ionized calcium in the medium has been investigated. A high concentration of ionized calcium outside the sarcoplasmic reticulum stimulates calcium efflux. Stimulation of calcium efflux from cardiac sarcoplasmic reticulum by high levels of ionized calcium outside the membranes is inhibited by magnesium. This inhibition can be overcome at very high concentrations of calcium in the medium. This resembles the magnesium inhibition of calcium triggered calcium release from skinned cardiac muscle fibres, which can also be overcome by increasing the concentration of calcium in the medium. Ouabain at 10 −6 m and verapamil at 10 −5 m have no effet on the stimulation of calcium efflux by calcium.
Published Version
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