Amylase release from streptolysin O-permeabilized pancreatic acinar cells. Effects of Ca2+, guanosine 5'-[γ-thio]triphosphate, cyclic AMP, tetanus toxin and botulinum A toxin

Abstract

The molecular requirements for amylase release and the intracellular effects of botulinum A toxin and tetanus toxin on amylase release were investigated using rat pancreatic acinar cells permeabilized with streptolysin O. Micromolar concentrations of free Ca2+ evoked amylase release from these cells. Maximal release was observed in the presence of 30 μM free Ca2+. Ca2+-stimulated, but not basal, amylase release was enhanced by guanosine 5'-[γ-thio]triphosphate (GTP[S]) (3-4 fold) or cyclic AMP (1.5-2 fold). Neither the two-chain forms of botulinum A toxin and tetanus toxin, under reducing conditions, nor the light chains of tetanus toxin, inhibited amylase release triggered by Ca2+, or combinations of Ca2+ + GTP[S] or Ca2+ + cAMP. The lack of inhibition was not due to inactivation of botulinum A toxin or tetanus toxin by pancreatic acinar cell proteolytic enzymes, as toxins previously incubated with permeabilized pancreatic acinar cells inhibited Ca2+-stimulated [3H]noradrenaline release from streptolysin O-permeabilizid adrenal chromaffin cells. These data imply that clostridial neurotoxins inhibit a Ca2+-dependent mechanism which promotes exocytosis in neural and endocrine cells, but not in exocrine cells.