THAPSIGARGIN-INDUCED CA2+ RELEASE FROM SARCOPLASMIC-RETICULUM AND ASOLECTIN VESICLES

Thapsigargin, an inhibitor of several isoforms of the Ca2+-ATPase protein, has been used in many cell preparations to induce an increase in cytosolic Ca2+ concentration purportedly by inhibition of the catalytic cycle. We report in this paper, that thapsigargin induces rapid Ca2+ release from sarcoplasmic reticulum vesicles at concentrations higher than those required to inhibit ATPase activity. Thapsigargin also induces a similar concentralion-dependent release in Ca2+-loaded asolectin liposomes devoid of any protein. These data suggest that Ca2+ release induced by micromolar concentrations of thapsigargin is due to an ionophoric effect on the lipid membrane.