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Comparison of [ 3 H]Phosphatidylinositol and [ 3 H]Phosphatidylinositol 4,5‐Bisphosphate Hydrolysis in Postmortem Human Brain Membranes and Characterization of Stimulation by Dopamine D1 Receptors
Author(s) -
Pacheco Mary A.,
Jope Richard S.
Publication year - 1997
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 - 10.1046/j.1471-4159.1997.69020639.x
Subject(s) - phosphatidylinositol , phosphatidylinositol 4,5 bisphosphate , phospholipase c , receptor , signal transduction , biochemistry , microbiology and biotechnology , dopamine receptor , dopamine , g protein , chemistry , biology , endocrinology
Assessing the function of the phosphoinositide signal transduction system in membranes prepared from postmortem human brain by measuring the hydrolysis of exogenous labeled phosphoinositides has been applied to studies of a variety of CNS disorders in recent years. Two issues concerning such studies were addressed in the current investigation: how do [ 3 H]phosphatidylinositol and [ 3 H]phosphatidylinositol 4,5‐bisphosphate compare as substrates, and how do dopamine D1 receptors influence phosphoinositide signaling? Comparisons of [ 3 H]phosphatidylinositol and [ 3 H]phosphatidylinositol 4,5‐bisphosphate hydrolysis stimulated by guanosine‐5′‐ O ‐(3‐thiotriphosphate)‐activated G proteins and by several receptor agonists demonstrated that in most cases each substrate gave similar relative results in membranes prepared from prefrontal cortices of six individuals. However, using optimal assay conditions, [ 3 H]phosphatidylinositol produced a greater signal‐to‐noise ratio compared with [ 3 H]phosphatidylinositol 4,5‐bisphosphate. Dopamine D1 receptors were demonstrated to be directly coupled to phosphoinositide hydrolysis in human brain membranes, and this response was shown to be mediated by the G q/11 G protein subtype and by the β‐subtype of phospholipase C. Therefore, these results demonstrate that [ 3 H]phosphatidylinositol is a suitable substrate to measure phosphoinositide hydrolysis in human brain membranes and that dopamine D1 receptors directly stimulate this signaling system.