A Galphas protein-coupled membrane receptor, distinct from the classical oestrogen receptor, transduces rapid effects of oestradiol on [Ca2+]i in female rat distal colon.
We examined the hypothesis whether rapid non-genomic effects of oestradiol (E2) on [Ca(2+)](i) are mediated via a membrane-located oestrogen receptor (ER) and further elucidated the signalling pathways involved in rapid non-genomic effects of E2 on [Ca(2+)](i) in distal colonic crypts. Basal [Ca(2+)](i) was significantly increased, within minutes, in response to physiological concentrations of E2. Oestradiol linked to bovine serum albumin (E2-BSA), which renders the E2 membrane impermeable, rapidly increased [Ca(2+)](i) suggesting mediation by a membrane surface receptor. A classical ER is not involved however, as no inhibition of either the E2 or E2-BSA [Ca(2+)](i) response was seen in the presence of the classical ER antagonist ICI 182,780. Treatment with the Galphas inhibitor cholera toxin abolished both E2 and E2-BSA induced Ca(2+) increases. In contrast, treatment with pertussis toxin, an inhibitor of Galphai and Galphao, had no inhibitory effect. Following subsequent additions of E2 and E2-BSA, no further increases in [Ca(2+)](i) were observed, indicating receptor desensitisation. The E2-induced increase in [Ca(2+)](i) was completely abolished by the PKCdelta-specific inhibitor rottlerin, whereas Go6976, an inhibitor of Ca(2+)-sensitive PKC isoforms, was without inhibitory effect. The phospholipase A2 antagonist, quinacrine, and the COX1 inhibitor, indomethacin, abolished the E2-induced increase in [Ca(2+)](i). MAP kinase activation is not involved in rapid stimulatory effects of E2 on [Ca(2+)](i) as the specific inhibitor PD98059 did not inhibit the E2 response. These results demonstrate that rapid E2-induced stimulation of [Ca(2+)](i), in femal rat distal colonic crypts, occurs via a CTx-sensitive Galphas-coupled membrane receptor distinct from the classical ER. PKCdelta and fatty acids are involved in the E2 signalling pathway. In contrast, PKCalpha and MAP kinase are not required.
Doolan
Christina M
CM
Department of Physiology, Biosciences Institute, University College Cork, Ireland. c.doolan@ucc.ie
Harvey
Brian J
BJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002772:Cholera Toxin / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D037342:Pertussis Toxin / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism* / Q000502:physiology; D011960:Receptors, Estrogen; D015398:Signal Transduction
D004791:Enzyme Inhibitors; D011956:Receptors, Cell Surface; D011960:Receptors, Estrogen; D004958:Estradiol; D002772:Cholera Toxin; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D002118:Calcium