AJP - Cell Physiology, Vol 267, Issue 5 C1329-C1337, Copyright © 1994 by American Physiological Society
Endothelin receptor in osteoblastic cells is coupled to multiple messenger signals
J. Green, O. Foellmer, C. R. Kleeman and M. M. Basic
Laboratory of Membrane Biology, Cedars-Sinai Medical Center, University of California School of Medicine, Los Angeles 90048.
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.
