Effect of Electrical Stimulation on Uptake and Release of Calcium by the Endoplasmic Reticulum

Abstract

OVER the past decade the concept has been developed that Ca⁺⁺ is a mediator of the so-called excitation-contraction coupling in muscle contraction and that the ‘calcium pump’ of the endoplasmic reticulum is responsible for relaxation^1–6. According to this concept the electrical excitation of muscle membrane releases Ca⁺⁺ from the endoplasmic reticulum and the released Ca⁺⁺ in turn triggers myofibrils to contract. Relaxation then occurs when the released Ca⁺⁺ is again taken up by the endoplasmic reticulum. However, as yet, no experimental evidence is available which directly supports the concept that following membrane excitation there is a release of Ca⁺⁺. In this communication, experimental results are presented which provide direct evidence in support of the concept that electrical stimulation releases stored Ca⁺⁺ from the endoplasmic reticulum and that the cessation of electrical stimulation is followed by re-uptake of Ca⁺⁺ by this system.