Endothelin receptor in osteoblastic cells is coupled to multiple messenger signals.
We analyzed the functional characteristics of endothelin (ET) peptides in the osteoblastic UMR-106 cells by studying receptor binding as well as dose-response curves for ET-1 and ET-3 on two biological responses: 1) induction of Ca2+ transients and 2) activation of the Na(+)-H+ exchanger. ET specifically binds to a single class of receptor with a rank order of affinity ET-1 >> ET-3. ET-1 and ET-3 dose dependently stimulated a rise in intracellular Ca2+ ([Ca2+]i), with ET-1 being two orders of magnitude more potent than ET-3 [50% effective concentration (EC50) = 8 x 10(-10) and 9 x 10(-8) M for ET-1 and ET-3, respectively; P < 0.01]. The effect of ET-1 on [Ca2+]i was 90% inhibitable by the ETA antagonist BQ-123. The activity of Na(+)-H+ exchange was studied by using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein as well as by 22Na+ fluxes. ET-1 and ET-3 activated the exchange in a concentration-dependent manner and with similar potencies (EC50 approximately 10(-10) M). The action of ETs on Na(+)-H+ exchange was mimicked neither by phorbol esters nor by Ca2+ ionophores. It was, however, blocked by BQ-123 as well as by the protein tyrosine kinase inhibitor genistein. We conclude that in UMR-106 cells, a single ET receptor subtype is coupled to multiple effectors, a Ca2+ message system and a tyrosine-kinase system which, in turn, activates the Na(+)-H+ exchanger.
Laboratory of Membrane Biology, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048.
J
J
Green
O
O
Foellmer
C R
CR
Kleeman
M M
MM
Basic
D000818:Animals; D002118:Calcium / Q000378:metabolism; D016232:Endothelins / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D010006:Osteoblasts / Q000378:metabolism* / Q000473:pathology; D012516:Osteosarcoma / Q000473:pathology; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D017466:Receptors, Endothelin / Q000378:metabolism*; D015290:Second Messenger Systems; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016232:Endothelins; D017466:Receptors, Endothelin; D017923:Sodium-Hydrogen Exchangers; D011493:Protein Kinase C; D002118:Calcium