Sequential activation of different Ca 2+ entry pathways upon cholinergic stimulation in mouse pancreatic acinar cells

1 We have studied capacitative calcium entry (CCE) under different experimental conditions in fura‐2‐loaded mouse pancreatic acinar cells by digital microscopic fluorimetry. CCE was investigated during [Ca 2+ ] i decay after cell stimulation with a supramaximal concentration of ACh (10 μM) or during Ca 2+ readmission in Ca 2+ ‐depleted cells (pretreated with thapsigargin or ACh). 2 La 3+ and Zn 2+ (100 μM) inhibited CCE during Ca 2+ readmission but had negligible effects during ACh decay. In contrast flufenamic acid (100 μM), an inhibitor of non‐selective cation channels, genistein (10 μM), a broad‐range tyrosine kinase inhibitor, and piceatannol (10 μM), an inhibitor specific for non‐receptor Syk tyrosine kinase, inhibited CCE during ACh decay but not during Ca 2+ reintroduction. 3 Simultaneous detection of Mn 2+ entry and [Ca 2+ ] i measurement showed that, in the presence of extracellular calcium, application of 100 μM Mn 2+ during ACh decay resulted in manganese influx without alteration of calcium influx, whilst when applied during Ca 2+ readmission, Mn 2+ entry was significantly smaller and induced a clear inhibition of CCE. 4 Application of the specific protein kinase C inhibitor GF109293X (3 μM) reduced CCE in Ca 2+ ‐depleted cells, whereas the activator phorbol 12‐myristate, 13‐acetate (3 μM) increased Ca 2+ entry. 5 Based on these results we propose that cholinergic stimulation of mouse pancreatic acinar cells induces Ca 2+ influx with an initial phase operated by a non‐specific cation channel, sensitive to flufenamic acid and tyrosine kinase inhibitors but insensitive to lanthanum and divalent cations, followed by a moderately Ca 2+ ‐selective conductance inhibited by lanthanum and divalent cations.