Calcium mediates the interconversion between two states of the liver inositol 1,4,5-trisphosphate receptor

J Biol Chem. 1990 Oct 15;265(29):17478-85.

Abstract

D-myo-Inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) regulates intracellular Ca2+ by mobilizing Ca2+ from a non-mitochondrial store. We have investigated the effects of Ca2+ on the binding of [32P]Ins (1,4,5)P3 to permeabilized rat hepatocytes and a liver plasma membrane-enriched fraction. Increasing the free Ca2+ concentration in the medium from 0.1 nM to 0.7 microM increased the capacity of a high affinity binding component (KD = 2-3 nM) in permeabilized cells by a factor of 10. If the membrane fraction was preincubated at 37 degrees C before binding was measured at 4 degrees C, all of the Ins(1,4,5)P3 receptors were transformed to a low affinity state (KD = 65 +/- 12 nM, Bmax = 3.1 +/- 0.1 fmol/mg, n = 4). When 0.7 microM of Ca2+ was added, the receptors were totally transformed to a high affinity state (KD = 2.8 +/- 0.4 nM, Bmax = 2.7 +/- 0.4 fmol/mg, n = 4). The EC50 of the Ca2(+)-induced interconversion of the Ins(1,4,5)P3 receptor was 140 nM. This Ca2(+)-induced transformation of the Ins(1,4,5)P3 receptor from a low affinity to a high affinity state was associated with an inhibition of the Ins(1,4,5)P3-induced Ca2+ release in permeabilized hepatocytes. These data suggest that the Ins(1,4,5)P3-dependent hormones, by increasing the intracellular Ca2+ concentration, induce a reversible transformation of the receptor from its low affinity state, coupled to the Ca2+ release, to a desensitized high affinity state. Transformation of the receptor may play a role in the oscillatory release of Ca2+ observed in single isolated hepatocytes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Calcium / pharmacology*
  • Calcium Channels*
  • Cell Membrane / metabolism
  • Cell Membrane Permeability
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Female
  • Inositol 1,4,5-Trisphosphate / metabolism
  • Inositol 1,4,5-Trisphosphate / pharmacology*
  • Inositol 1,4,5-Trisphosphate Receptors
  • Kinetics
  • Liver / drug effects
  • Liver / metabolism*
  • Rats
  • Rats, Inbred Strains
  • Receptors, Cell Surface / drug effects
  • Receptors, Cell Surface / metabolism*
  • Receptors, Cytoplasmic and Nuclear*
  • Vasopressins / pharmacology*

Substances

  • Calcium Channels
  • Inositol 1,4,5-Trisphosphate Receptors
  • Receptors, Cell Surface
  • Receptors, Cytoplasmic and Nuclear
  • Vasopressins
  • Inositol 1,4,5-Trisphosphate
  • Calcium