title: Forskolin refractoriness. Exposure to the diterpene alters guanine nucleotide-dependent adenylate cyclase and calcium-uptake activity of cells cultured from the rat aorta.
abstract: Cells with the morphological properties of endothelial cells were cultured from the rat aorta. The cultured cells accumulated 45Ca2+ from the medium in a manner which was stimulated by forskolin and by 8-bromo-cyclic AMP. Pretreating the cultures for 20 h with forskolin diminished forskolin-dependent Ca2+-uptake activity. Adenylate cyclase activity of cultured cell homogenates was stimulated by guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) and forskolin, and by isoprenaline in the presence, but not in the absence, of guanine nucleotide. p[NH]ppG increased forskolin sensitivity and caused a leftward shift in the forskolin dose-response curve. Pretreating the cultured cells with forskolin for 20 h, conditions that decreased forskolin-dependent Ca2+ uptake, increased basal and guanine nucleotide-dependent adenylate cyclase activity, but not forskolin-dependent activity determined in the absence of p[NH]ppG. Forskolin pretreatment diminished p[NH]ppG's capacity to increase forskolin sensitivity, but did not have a significant effect on either the sensitivity of adenylate cyclase to p[NH]ppG or its responsiveness to isoprenaline. These results suggest that the Ca2+-uptake mechanism is cyclic AMP-dependent and that guanine nucleotides mediated forskolin-dependent cyclic AMP production by the intact cells. In addition, there may be different guanine nucleotide requirements for hormone-receptor coupling and forskolin activation.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001013:Aorta, Thoracic / Q000166:cytology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology; D004727:Endothelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006150:Guanine Nucleotides; D007545:Isoproterenol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D006150:Guanine Nucleotides; D005576:Colforsin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium