Rapid increases in inositol 1,4,5-trisphosphate, inositol 1,3,4,5-tetrakisphosphate and cytosolic free Ca 2+ in agonist-stimulated pancreatic acini of the rat. Effect of carbachol, caerulein and secretin

Abstract

We compared the time course of increases in isomers of inositol trisphosphate [Ins(1,4,5)P 3] and Ins(1,3,4)P 3] and the tetrakisphosphate [Ins(1,3,4,5)P 4] with changes in cytosolic free Ca 2+ ([Ca 2+](i)) in dispersed pancreatic acini of the rat. There were rapid (5s) increases in Ins(1,4,5)P 3 and Ins(1,3,4,5)P 4 in response to carbachol, caerulein and secretin, whereas Ins(1,3,4)P 3 increased more slowly. All three secretagogues induced increases in [Ca 2+](i), which reached a peak at 15-20 s. Our results indicate that the very rapid formation of Ins(1,4,5)P 3 is compatible with its second-messenger role in the initial elevation of [Ca 2+](i).