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Inositol Phospholipid Hydrolysis in Rat Cerebral Cortical Slices: II. Calcium Requirement
Author(s) -
Kendall David A.,
Nahorski Stefan R.
Publication year - 1984
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1984.tb02799.x
Subject(s) - egta , nitrendipine , phosphatidylinositol , inositol , calcium , chemistry , inositol phosphate , inositol trisphosphate , histamine , phospholipid , biochemistry , endocrinology , medicine , receptor , biology , membrane , kinase , organic chemistry
The calcium requirement for agonist‐dependent breakdown of phosphatidylinositol and polyphos‐phoinositides has been examined in rat cerebral cortex. The omission of added Ca 2+ from the incubation medium abolished [ 3 H]inositol phosphate accumulation from prelabelled phospholipid induced by histamine, reduced that due to noradrenaline and 5‐hydroxytryptamine, but did not affect carbachol‐stimulated breakdown. EC 50 values for agonists were unaltered in the absence of Ca 2+ . Removal of Ca 2+ by preincubation with EGTA (0.5 m M ) abolished all responses, but complete restoration was achieved by replacement of Ca 2+ . The EC 50 for Ca 2+ for histamine‐stimulated [ 3 H]inositol phosphate accumulation was 80 μ M . Noradrenaline‐stimulated breakdown was antagonised by manganese (IC 50 1.7 m M ), but not by the calcium channel blockers nitrendipine or nimodipine (30 μ M ). The calcium ionophore A23187 stimulated phosphatidylinositol/polyphosphoinositide hydrolysis with an EC 50 of 2 μ M , and this response was blocked by EGTA. Omission of Ca 2+ or preincubation with EGTA or Mn 2+ (EC 50 = 230 μ M ) greatly enhanced the incorporation of [ 3 H]inositol into phospholipids. The IC 50 for Ca 2+ in inhibiting incorporation was 25 μ M . The results show that different receptors mediating phosphatidylinositol/ polyphosphoinositide breakdown in rat cortex have quantitatively different Ca 2+ requirements, and it is suggested that rigid opinions regarding phosphatidylinositol/ polyphosphoinositide breakdown as either cause or effect of calcium mobilisation in rat cortex are inappropriate.