Premium
Positive and negative coupling of the endothelin ET A receptor to Ca 2+ ‐permeable channels in rabbit cerebral cortex arterioles
Author(s) -
Guibert C.,
Beech D. J.
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.843ad.x
Subject(s) - chemistry , biophysics , patch clamp , endothelin 1 , thapsigargin , endothelin receptor , medicine , depolarization , endocrinology , membrane potential , fura 2 , voltage clamp , extracellular , receptor , biology , biochemistry , cytosol , enzyme
1 Arteriolar segments were isolated from pial membrane and studied within 10 h. Current‐clamp and voltage‐clamp measurements were made by patch‐clamp recording from smooth muscle cells within arterioles. [Ca 2+ ] i was measured from the smooth muscle cell layer by digital imaging of emission from fura‐PE3 which was loaded into arterioles by pre‐incubation with the acetoxymethyl ester derivative. The external diameter of arterioles was measured using a video‐dimension analyser. 2 Endothelin‐1 (ET1) was a potent constrictor of isolated arterioles and induced a sustained depolarization up to ‐27 mV and reduced membrane resistance (EC 50 140‐170 pm). At a constant holding potential of ‐60 mV ET‐1 induced a transient followed by a sustained inward current. ET1 inhibited L‐type voltage‐dependent Ca 2+ current. 3 ET1 induced a transient followed by sustained elevation of [Ca 2+ ] i . The sustained effect was dependent on extracellular Ca 2+ . It occurred at a constant holding potential of ‐60 mV and was not inhibited by the Ca 2+ antagonists nicardipine (1 μM) or D600 (10 μM). Thapsigargin (1 μM) completely depleted Ca 2+ from caffeine‐ and ET1‐sensitive sarcoplasmic reticulum but did not inhibit the ET1‐induced sustained elevation of [Ca 2+ ] i . ET1 effects on [Ca 2+ ] i were prevented by the ET A receptor antagonist BQ123 (cyclo‐D‐Asp‐Pro‐D‐Val‐Leu‐D‐Trp). 4 The data suggest that ET A receptors are negatively coupled to L‐type Ca 2+ channels and positively coupled to receptor‐operated Ca 2+ ‐permeable channels. Inhibition of L‐type Ca 2+ channel activity may suppress autoregulation, and Ca 2+ influx through receptor‐operated channels may have a major functional role in the potent long‐lasting constrictor effect of endothelin‐1 in the cerebral microcirculation.