Ca²⁺ signaling through secretagogue and growth factor receptors on pancreatic AR42J cells

Intracellular signaling by an increase in [Ca²⁺]_i was observed in pancreatic AR42J cells in response to agonists whose receptors are G-protein coupled including cholecystokinin (CCK), bombesin, carbachol, substance P, pituitary adenylate cyclase activating peptide (PACAP), bradykinin, ATP, calcitonin gene related peptide (CGRP), and in response to growth factors EGF and FGF whose receptors are tyrosine kinases. The response to growth factors was smaller both in magnitude and in the percentage of cells responding but was independent of extracellular Ca²⁺. CCK and carbachol induced sizeable increases in inositol phosphates while growth factors did not. The responses to both carbachol and EGF, however, were blocked by the phospholipase C inhibitor U73122. The tyrosine kinase inhibitor, genestein, blocked the response to EGF but not that to CCK. These data are consistent with two types of signaling mechanisms in AR42J cells. Secretagogues act on receptors which couple through G proteins to induce a large amount of inositol phosphate production and subsequent intracellular Ca²⁺ mobilization. Growth factors act on receptors which signal through tyrosine kinase activity and in this cell type produced limited amounts of inositol phosphate and a smaller increase in intracellular Ca²⁺.