Decreased endothelin binding and [Ca2+]i signaling in microvessels of DOCA-salt hypertensive rats.
OBJECTIVE
The deoxycorticosterone acetate (DOCA)-salt model of hypertension is characterized by elevated vascular endothelin-1 (ET-1) and by reduced contraction to ET-1 in isolated mesenteric small arteries. The decreased contraction to ET-1 may be a compensatory mechanism caused by elevations in ET-1 and arterial pressure. The present study was designed to determine whether down-regulation of endothelin receptors or altered Ca2+ signaling contribute to the decreased contraction to ET-1.


RESULTS
Contraction to ET-1 (10 to 10 mol/l) was significantly reduced in isolated mesenteric small arteries (87-286 microm intraluminal diameter) from DOCA-salt rats compared with placebo rats. Membrane protein was obtained for measurement of [125I]ET-1 receptor binding and ET receptor expression. Maximum binding was significantly reduced in vascular membranes from DOCA-salt rats (670 +/- 71 fmol/mg protein) compared with placebo rats (1165 +/- 75 fmol/mg protein), but binding affinity was unchanged. Conversely, ETA receptor protein was increased in DOCA-salt rat vessels. To assess Ca2+ signaling, freshly dissociated mesenteric small artery smooth muscle cells were loaded with fura-2 for measurement of the average myoplasmic free Ca2+ concentration ([Ca2+ ] ). The ET-1 (10 mol/l) induced increase in [Ca2+ ] was significantly less in cells from DOCA-salt rats compared with from placebo rats. This effect was not due to a loss of L-type Ca2+ channels since expression was increased in membrane protein from DOCA-salt rats compared with placebo rats, as measured by Western blot analysis.


CONCLUSIONS
These findings indicate that decreases in receptor binding and Ca2+ signaling contribute to the impaired contraction to ET-1 in DOCA-salt hypertensive rats. However, these changes are not due to reduced expression of ETA receptors or L-type Ca2+ channels.
Vascular Biology Center, Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, Georgia 30912, USA.
Mariela M
MM
Molero
Ararat D
AD
Giulumian
Vikram B
VB
Reddy
Lynda M
LM
Ludwig
Jennifer S
JS
Pollock
David M
DM
Pollock
Nancy J
NJ
Rusch
Leslie C
LC
Fuchs
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling; D003900:Desoxycorticosterone; D019332:Endothelin-1 / Q000494:pharmacology; D016232:Endothelins / Q000378:metabolism*; D006973:Hypertension / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology*; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism* / Q000503:physiopathology*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000378:metabolism; D012965:Sodium Chloride; D014661:Vasoconstriction
D020746:Calcium Channels, L-Type; D019332:Endothelin-1; D016232:Endothelins; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D003900:Desoxycorticosterone; D012965:Sodium Chloride; D002118:Calcium