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

GABABreceptors regulate the intracellular Ca2+concentration ([Ca2+]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 [Ca2+]iis not known. The purpose of this study was to investigate the expression of GABABreceptors, a subclass of receptors to the inhibitory neurotransmitterγ-aminobutyric acid (GABA), in cultured human aortic endothelial cells (HAECs), and to explore if altering receptor activation modified [Ca2+]iand endothelial nitric oxide synthase (eNOS) translocation. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABAB1and GABAB2in cultured HAECs. The effects of GABABreceptors on [Ca2+]iin cultured HAECs were demonstrated using fluo-3. The influence of GABABreceptors on eNOS translocation was assessed by immunocytochemistry. Both GABAB1and GABAB2mRNA and protein were expressed in cultured HAECs, and the GABAB1and GABAB2proteins were colocated in the cell membrane and cytoplasm. One hundredμM baclofen caused a transient increase of [Ca2+]iand eNOS translocation in cultured HAECs, and the effects were attenuated by pretreatment with the selective GABABreceptor antagonists CGP46381 and CGP55845. GABABreceptors are expressed in HAECs and regulate the [Ca2+]iand eNOS translocation. Cultures of HAECs may be a usefulin vitromodel for the study of GABABreceptors and vascular biology.