Ca2+ and cyclic nucleotide dependence of amylase release from isolated rat pancreatic acinar cells rendered permeable by intense electric fields

Abstract

Enzyme digestion of rat pancreatic tissue yielded a preparation of isolated acinar cells, over 90% of which excluded trypan blue. These isolated cells responded to a variety of secretagogues, the responses being sensitive to the removal of extracellular calcium, increasing extracellular magnesium, and by trifluoperazine, an antagonist of Ca-dependent processes. When exposed to intense electric fields, isolated acinar cells became permeable to CaEGTA and MgATP, these markers gaining access to over 60% of the intracellular milieu within minutes. The accessibility to these markers seemed independent of the ionised Ca2+ level. Less than 0.5% of the cellular amylase was released when cells were rendered leaky in a medium containing about 10(-9) M Ca2+, but typically 4% was released when the Ca2+ level was subsequently raised to 10(-5)M levels, the EC50 for Ca2+ being 2 microM. This amount of amylase released was comparable to the amounts secreted from intact cells in response to a variety of agonists. The cytosolic marker lactate dehydrogenase was also released from leaky cells, but the extent was independent of Ca2+ concentration. No amylase was released at 10(-7)M Ca2+ when permeable cells were exposed to cyclic 3',5'-AMP or cyclic 3',5'-GMP. The calcium activation curve for amylase release seemed to be independent of cyclic nucleotides, but was markedly increased in both the extent of release and apparent affinity for Ca2+ in the presence of the phorbol ester 12-0-tetradecanoyl phorbol 13 acetate. These results suggest that when "functionally normal" isolated acinar cells are rendered permeable, Ca2+-but not cyclic nucleotides-acts as a second messenger for amylase secretion, and furthermore that protein kinase C may be involved in the secretory process.