Agonists trigger Ca*+ waves and oscillations in exocrine gland cells. Our confocal Ca*+ imaging revealed three distinct phases during the Ca*+ waves in the rat pancreatic acinar cell. Rises in Ca*+ concentration were initiated at a small trigger zone, or T zone, in the granular area; then, Ca*+ waves rapidly spread within the area and, at high agonist concentrations, propagated slowly toward the basal pole. Injection of inositol 1, 4, 5trisphosphate(lP $ or Ca*+ from patch pipettes demonstrated the presence of high sensitivity IP3 receptors at the T zone, Ca*+-induced Ca*+ release channels in the granular area, and low sensitivity IP3 receptors in the basal area. The IP3 receptors at the T zone appeared to generate autonomous Ca*+ spikes and to initiate patterned Ca*+ oscillations. Thus, heterogeneous cytosolic localization of Ca*+ release channels plays a key role in Caz+ waves and oscillations.