4-Aminobutyrate Can Be Released Exocytotically from Guinea-Pig Cerebral Cortical Synaptosomes |
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Authors: | Talvinder S Sihra David G Nicholls |
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Institution: | Department of Biochemistry, University of Dundee, Dundee, Scotland |
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Abstract: | Guinea-pig synaptosomes possess two functional pools of 4-aminobutyrate (GABA). One is rapidly labelled by added 14C]GABA, is steadily released in a Ca2+-independent manner when the Na+ electrochemical potential across the plasma membrane is collapsed, and is depleted by the GABA analogue 2,4-diaminobutyrate (DABA), all of which is consistent with a cytosolic location. A second, noncytosolic compartment only slowly equilibrates with exogenous 14C]GABA, is not depleted by DABA, but can release 350 pmol of endogenous GABA/mg of protein (8% of the total intrasynaptosomal GABA) within 15 s of depolarization in the presence of Ca2+. Ca2+-independent release occurs by thermodynamic reversal of the plasma membrane uptake pathway following artifactually prolonged depolarization, whereas Ca2+-dependent release is consistent with physiological exocytosis from vesicular stores. |
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Keywords: | 4-Aminobutyrate Synaptosomes Membrane potential Exocytosis Calcium |
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