Effect of G. breve toxin on calcium uptake and ATPase activity of sarcoplasmic reticulum vesicles

Abstract

The major toxin derived from the red-tide dinoflagellate, Gymnodinium breve, inhibited Ca 2+ uptake by sarcoplasmic reticulum vesicles obtained from skeletal muscles of the rabbit. G. breve toxin concentrations > 4 μg/ml or exposure longer than 5 min produced ∼ 25–40% inhibition of Ca 2+ uptake, independent of external Ca 2+ concentration or the presence of oxalate. The efflux of Ca 2+, however, was stimulated by G. breve toxin only in the absence of oxalate ions. The Ca 2+-Mg 2+ dependent ATPase activity was enhanced by G. breve toxin by ∼ 20–40% depending on the toxin concentration and duration of exposure. It is suggested that G. breve toxin affects the stability of the sarcoplasmic reticulum membrane at Ca 2+-binding sites.