Thapsigargin-induced Ca2+ release from sarcoplasmic reticulum and asolectin vesicles.

Thapsigargin, an inhibitor of several isoforms of the Ca(2+)-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 concentration-dependent release in Ca(2+)-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.