GABABReceptors Expressed in Human Aortic Endothelial Cells Mediate Intracellular Calcium Concentration Regulation and Endothelial Nitric Oxide Synthase Translocation

GABA B receptors regulate the intracellular Ca 2+ concentration ([Ca 2+ ] i ) in a number of cells (e.g., retina, airway epithelium and smooth muscle), but whether they are expressed in vascular endothelial cells and similarly regulate the [Ca 2+ ] i is not known. The purpose of this study was to investigate the expression of GABA B receptors, a subclass of receptors to the inhibitory neurotransmitter γ -aminobutyric acid (GABA), in cultured human aortic endothelial cells (HAECs), and to explore if altering receptor activation modified [Ca 2+ ] i and endothelial nitric oxide synthase (eNOS) translocation. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABA B1 and GABA B2 in cultured HAECs. The effects of GABA B receptors on [Ca 2+ ] i in cultured HAECs were demonstrated using fluo-3. The influence of GABA B receptors on eNOS translocation was assessed by immunocytochemistry. Both GABA B1 and GABA B2 mRNA and protein were expressed in cultured HAECs, and the GABA B1 and GABA B2 proteins were colocated in the cell membrane and cytoplasm. One hundred μ M baclofen caused a transient increase of [Ca 2+ ] i and eNOS translocation in cultured HAECs, and the effects were attenuated by pretreatment with the selective GABA B receptor antagonists CGP46381 and CGP55845. GABA B receptors are expressed in HAECs and regulate the [Ca 2+ ] i and eNOS translocation. Cultures of HAECs may be a useful in vitro model for the study of GABA B receptors and vascular biology.