title: Platelet-activating factor-induced homologous and heterologous desensitization in cultured vascular smooth muscle cells.
abstract: Intracellular free Ca2+ concentrations were monitored in vascular smooth muscle cells (VSMC) using the Ca2+-sensitive dye fura II. Superfusion of VSMC with platelet-activating factor (S-PAF; 1-100 nM) increased cytosolic Ca2+ in a dose-dependent manner. The response was transient and returned to base line even though the agonist was still present. A second, higher dose of PAF did not elicit a response. The inactive optical isomer, R-PAF, was ineffective suggesting that the S-PAF response is specific and receptor-mediated. Pretreatment of VSMC with PAF attenuated angiotensin II-stimulated Ca2+ mobilization but not vasopressin-stimulated Ca2+ mobilization. Treatment of VSMC with PAF (10 nM) stimulated inositol trisphosphate and inositol tetrakisphosphate formation above control by 260 +/- 15% and 195 +/- 11%, respectively. Diacylglycerol levels also rose during PAF stimulation and remained increased over 15 min. Pretreatment of VSMCs with phorbol-12,13-myristate acetate (10 nM) for 30 min abolished both the PAF- and angiotensin II-induced increases in cytosolic Ca2+, but not the vasopressin-induced increase. Pretreatment of VSMC with dioctanoylglycerol (10 microM) abolished the S-PAF-, angiotensin II-, and vasopressin-induced elevation in cytosolic Ca2+. We propose that this desensitization is possibly mediated by diacylglycerol formed in response to PAF.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
authors.forename: U S
authors.initials: US
authors.lastname: Schwertschlag
authors.forename: A R
authors.initials: AR
authors.lastname: Whorton
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D001572:Benzofurans; D004075:Diglycerides; D005456:Fluorescent Dyes; D007295:Inositol Phosphates; D010972:Platelet Activating Factor; D014667:Vasopressins; D000804:Angiotensin II; D015544:Inositol 1,4,5-Trisphosphate; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D016257:Fura-2