Actions of inositol phosphates on Ca2+ pools in guinea-pig hepatocytes

Abstract

In permeabilized hepatocyes, inositol 1,4,5-triphosphate, inositol 2,4,5-trisphosphate and inositol 4,5-bisphosphate induced rapid release of Ca2+ from an ATP-dependent, non-mitochondrial vesicular pool, probably endoplasmic reticulum. The order of potency was inositol 1,4,5-trisphosphate > inositol 2,4,5-triphosphate > inositol 4,5-bisphosphate. The Ca2+-releasing action of inositol 1,4,5-trisphosphate is not inhibited by high [Ca2+], nor is it dependent on [ATP] in the range of 50 .mu.M-1.5 mM. A role for inositol 1,4,5-trisphosphate as a 2nd messenger in hormone-induced Ca2+ mobilization is suggested, and a specific receptor is involved in the Ca2+-release mechanism.