[Ca2+](i)-dependent secretory responses (salivary chromogranin A, flow andprotein) to alpha- and beta-adrenergic stimulation in isolated and perfused rat submandibular glands

Chromogranin A-like immunoreactivity (CgA-like IR) is stored in the exocrin e cells in the granular convoluted tubule (GCT) in the rat submandibular gl and, and highly concentrated CEA-like IR (approximately 1 mM) is secreted i nto saliva in response to stimulation with phenylephrine, an alpha -adrener gic agonist, in the isolated and perfused rat submandibular gland. The stim ulation caused immediate and prominent increases in secretory responses (Cg A-like IR secretion, flow, and protein secretion). The secretory responses to 3 muM-phenylephrine were scarcely inhibited in a Ca2+-deficient environm ent, and were almost completely inhibited by 100 muM 2-aminoethoxydiphenyl borate (2-APB), an inhibitory modulator of 1, 4, 5 trisphosphate (IP3)-medi ated Ca2+ release from intracellular stores. These results are compatible w ith a view that mobilization of Ca2+ from the IP3-sensitive pool may prefer entially be involved in the secretory responses to alpha -adrenergic agonis t. The secretory responses to isoproterenol, beta -adrenergic agonist, rema ined almost unchanged in the Ca2+ deficient environment, and were markedly delayed by 100 muM 2-APB but were regained gradually after removal of 2APB and the agonist. Mobilization of Ca2+ from the pool may also be involved to facilitate synergistic signallings in the beta -adrenergic responses.