The effects of potentiators and of anticholinesterases on the kinetics of calcium uptake by isolated sarcoplasmic reticulum from the lobster and the rat

Abstract

1. 1. Ca 2+ uptake by vesicles of sarcoplasmic reticulum from lobster and rat muscle was measured spectrophotometrically. 2. 2. Uptake follows Michaelis-Menten kinetics. 3. 3. The activation energy for uptake is about 3400 cal. per mole Ca 2+. 4. 4. Lobster preparations contain a specific acetylcholinesterase and Ca 2+ uptake is inhibited by anticholinesterases; however, much more inhibitor is needed to block transport than to depress enzyme activity. 5. 5. Caffeine is a competitive inhibitor of Ca 2+ uptake, but the inhibition is probably not sufficient to account for the action of caffeine on intact muscle. 6. 6. Rat and lobster vesicles are remarkably similar in their kinetics and in their response to inhibitors.