The intracellular site of calcium activation of contraction in frog skeletal muscle

Abstract

Radioautography has been used to localize 45Ca in isotopieally labeled frog skeletal muscle fibers which had been quickly frozen during a maintained tetanus, a declining tetanus, or during the period immediately following a tetanus or a contracture. During a tetanus almost all of the myofibrillar 45Ca is localized in the region of the sareomere occupied by the thin filaments. The amount varies with the tension being developed by the muscle. The movement of calcium within the reticulum from the tubular portion to the terminal eisternae during the posttetanic period has a half-time of about 9 see at room temperature and a Q10 of about 1.7. Repolarization is not necessary for this movement. Evidence is given to support the notion that most calcium effiux from the cell occurs from the terminal eisternae into the transverse tubules. © 1970, Rockefeller University Press., All rights reserved.