DISTRIBUTION OF CA2-SURFACE( EXTRUSION SITES ON THE MOUSE PANCREATIC ACINAR CELL)

The localizations of Ca2+ extrusion sites in mouse pancreatic acinar c ells during elevation of the intracellular free calcium concentration ([Ca2+](i)) have been studied. During an agonist stimulated calcium el evation as well as when intracellular calcium is released from a 'cage d compound', Ca2+ is primarily extruded from the apical secretory pole of the cells in spite of different spatial patterns of [Ca2+](i), dif ferent sources of Ca2+, and the presence or absence of agonist, This i s most likely due to a relatively high density of calcium pumps in the secretory granule region, although it could be explained by calcium p umps in this part of the cell having different characteristics from th ose in the basal membrane. The intensity of Ca2+ extrusion in the apic al secretory pole is such that substantial (several millimoles per lit re) changes of the free calcium concentration in the lumen of the acin us can occur during agonist stimulation.