Cyclic ADP‐ribose and inositol 1,4,5‐trisphosphate mobilizes Ca²⁺ from distinct intracellular pools in permeabilized lacrimal acinar cells

Abstract

In permeabilized lacrimal acinar cells, cyclic ADPribose (cADP-ribose) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) release Ca 2+ in a dose dependent manner from distinct tbapsigargin-sensitive Ca 2+ pools. Ryanodine specifically blocks the Ca 2+ response to cADP-ribose, whereas heparin strongly reduces the response to Ins(1,4,5)P3 application. GTP causes a rapid Ca z+ release by a ryanodine-and heparin-insensitire mechanism and potentiates Ins(1,4,5)P 3 but not cADP-ribose evoked Ca 2+ release. It is estimated that cADP-ribose can release 16/xmol Ca2+/l cells, whereas Ins(1,4,5)P3 can mobilize 55/xmol Ca2+/l cells. The results suggest that cADP-ribose and Ins(1,4,5)P3 release Ca 2+ from distinct internal stores and that a third Ca 2+ pool exists which can selectively interact with the Ins(1,4,5)P3-sensitive Ca z+ store by a GTP-mediated process.