RECURRENT CA2-CELLS( SPIKES AS INTRACELLULAR SIGNALS FOR PHYSIOLOGICAL SECRETORY RESPONSES IN PANCREATIC ACINAR)

Analysis of competitive inhibition of tracer binding by unlabeled CCK- 8 was consistent with binding to two affinity states of CCK receptor o n isolated rat pancreatic acini, with the equilibrium dissociation con stants for the high- and low-affinity states equal to 15.2 pM and 3.5 nM respectively. Spatial and temporal dynamics of cytosolic concentrat ion of Ca2+, [Ca2+]c, were recorded by a digital image analyzing techn ique using Fura-2 Continuous stimuration of isolated acini with a phys iological concentration of cholecystokinin octapeptide (10 pM CCK-8) c aused recurrent Ca2+ spikes and a sustainable amylase output. These re sponses were both abolished in Ca2+-deficient environment. The stimula tion of the acini with a pharmacological (100 pM) concentration, howev er, induced a rapid [Ca2+]c increase followed by a gradual decay, and a rapid initial rise in amylase output followed by a gradual decay. In the Ca2+-deficient environment, the initial phases of responses remai ned but the second decay phases were selectively abolished. These resu lts indicate that the binding of CCK-g to the high-affinity state on t he acini induces recurrent Ca2+ spikes, which may maintain the sustain able secretory responses in the pancreatic acinar cells.