Distribution of gamma-aminobutyric acid receptors in cultured adrenergic and noradrenergic bovine chromaffin cells.
Fluorescence imaging techniques for recording cytosolic [Ca(2+)](i) from single chromaffin cells were used to characterize and discriminate between cell subpopulations containing gamma-aminobutyric acid (GABA)(A) and GABA(B) receptor subtypes. By combining this methodology with the immunoidentification of individual chromaffin cells using specific antibodies against tyrosine hydroxylase (TH), phenyl-etanolamine-N-methyl transferase (PNMT), and glutamic acid decarboxylase (GAD) linked to different fluorescent probes, we have been able to ascribe single-cell calcium responses to identified adrenergic and noradrenergic chromaffin cells. GAD enzyme is present in 30% of the chromaffin cell population, located primarily in adrenergic cells; 86% of GAD(+) cells were also PNMT(+). GAD expression was not correlated with the presence of GABA receptors. GABA-responsive cells were found with equal frequency in the GAD(+) and GAD(-) groups. However, the expression of GABA receptors was correlated with the adrenergic phenotype. [Ca(2+)](i) responses to GABA were found more frequently in adrenergic than in noradrenergic cells. GABA(A) receptors are more evenly distributed; about 90% of GABA-responsive cells have them. GABA(B) receptors have a more restricted distribution (present in 45% of responding cells). The coexpression of both GABA(A) and GABA(B) subtypes is the rule; only a minor subpopulation (about 12%) displays exclusively GABA(B) receptors. GABA receptor subtypes are distributed in a similar way when chromaffin cells are separated according to GAD(+)/GAD(-) or PNMT(+)/PNMT(-) classifications, with only minor differences. These data indicate that the intrinsic GABAergic system in the adrenal medulla is not designed as a paracrine model in which a group of cells specializes in transmitter synthesis and a different group serves as a specific target.
Castro
Enrique
E
Department of Biochemistry, Molecular Biology and Physiology, Faculty of Medicine and Health Sciences, University of Las Palmas de Gran Canaria, Las Palmas, Spain.
González
María Pilar
MP
Oset-Gasque
María Jesús
MJ
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D004837:Epinephrine / Q000096:biosynthesis / Q000502:physiology*; D005968:Glutamate Decarboxylase / Q000032:analysis / Q000096:biosynthesis; D009638:Norepinephrine / Q000096:biosynthesis / Q000502:physiology*; D010625:Phenylethanolamine N-Methyltransferase / Q000032:analysis / Q000096:biosynthesis; D018079:Receptors, GABA / Q000096:biosynthesis / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis / Q000096:biosynthesis; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid; D014446:Tyrosine 3-Monooxygenase; D010625:Phenylethanolamine N-Methyltransferase; D005968:Glutamate Decarboxylase; D009638:Norepinephrine; D004837:Epinephrine