CAPACITATIVE CA2+ INFLUX AND A CA2+ DEPENDENT NONSELECTIVE CATION PATHWAY ARE DISCRIMINATED BY GENISTEIN IN MOUSE PANCREATIC ACINAR-CELLS

We have investigated the effect of genistein on the hormone-stimulated Ca2+ influx and on a 28 pS nonselective cation channel in mouse pancreatic acinar cells using the Ca2+ indicator fluo-3 and the patch-clamp technique. The identity of the Ca2+ influx pathway has not been established in this cell type so far. Therefore we have investigated the Ca2+-dependent nonselective cation channel as a potential pathway for Ca2+ influx. ''Capacitative'' Ca2+ entry was induced by depletion of intracellular Ca2+ stores with 500nM acetylcholine or with the Ca2+ ATPase inhibitor 2,5-di-tert-butylhydroquinone. In the presence of 100 mu M genistein, Ca2+ release was unimpaired, whereas Ca2+ influx was reversibly suppressed. Patch-clamp experiments demonstrated that genistein had no effect on Ca2+-activated nonselective cation channels, the activity of which was measured in excised membrane patches (inside/out) or in the whole-cell configuration. Therefore we conclude that this 28 pS nonselective cation channel does not contribute to Ca2+ influx into mouse exocrine pancreatic cells. With the exception of genistein and tyrphostin 25, other tyrosine kinase inhibitors such as methyl-2,5-dihydroxycinnamate, lavendustin A, herbimycin A, and tyrphostin B56 were without effect on Ca2+ signalling. Thus, the involvement of tyrosine phosphorylation in the activation of the Ca2+ entry mechanism in mouse pancreatic acinar cells is unclear.