Subcellular distribution of Ca 2+ release channels underlying Ca 2+ waves and oscillations in exocrine pancreas

Abstract

Agonists trigger Ca 2+ waves and oscillations in exocrine gland cells. Our confocal Ca 2+ imaging revealed three distinct phases during the Ca 2+ waves in the rat pancreatic acinar cell. Rises in Ca 2+ concentration were initiated at a small trigger zone, or T zone, in the granular area; then, Ca 2+ waves rapidly spread within the area and, at high agonist concentrations, propagated slowly toward the basal pole. Injection of inositol 1,4,5-trisphosphate (IP 3) or Ca 2+ from patch pipettes demonstrated the presence of high sensitivity IP 3 receptors at the T zone, Ca 2+-induced Ca 2+ release channels in the granular area, and low sensitivity IP 3 receptors in the basal area. The IP 3 receptors at the T zone appeared to generate autonomous Ca 2+ spikes and to initiate patterned Ca 2+ oscillations. Thus, heterogeneous cytosolic localization of Ca 2+ release channels plays a key role in Ca 2+ waves and oscillations.