Dose-dependency in spatial dynamics of [Ca2+]c in pancreatic acinar cells

Spatial dynamics of cytosolic concentration of Ca2+, [Ca2+]c, in stimulus-secretion coupling of rat pancreatic acinar cell was monitored by a digital image analysing technique using Fura-2. When freshly isolated acini were stimulated with lower concentrations of CCK-8 (5-30 pM), [Ca2+]c increase began at the region beneath the basolateral membrane and the [Ca2+]c increase depended on the presence of extracellular Ca2+ ([Ca2+]o). CCK-8 at higher concentrations (100 pM and 1 nM), however, caused [Ca2+]c increase even in the absence of [Ca2+]o. Low concentrations of G-protein activator, NaF (10 mM or lower), caused [Ca2+]o-dependent increase in [Ca2+]c, whereas higher concentrations of NaF (15 mM or higher) increased [Ca2+]c in the absence of [Ca2+]o. These results are compatible with the view that G-protein activated by a physiological concentration of secretagogue accelerates Ca2+ entry. This process is in contrast to the process of Ca2+ release from intracellular stores, which can be predominant when pharmacological or toxic concentration of the secretagogue was applied.