title: Disparate effects of Ca channel blockade on afferent and efferent arteriolar responses to ANG II.
abstract: Previous reports have suggested that organic calcium antagonists only partially inhibit the renal hemodynamic actions of angiotensin II (ANG II). This study tested the hypothesis that the calcium antagonist-sensitive component of ANG II-induced vasoconstriction is localized at a preglomerular site. Videomicroscopic measurements of vascular dimension were performed on in vitro blood-perfused juxtamedullary nephrons from captopril-treated rats. Under control conditions, afferent and efferent arteriolar diameters averaged 23.0 +/- 1.6 and 21.2 +/- 2.2 microns, respectively. Topical application of 0.1 nM ANG II decreased the diameters of afferent (-17 +/- 2%) and efferent (-15 +/- 3%) arterioles. Both 50 microM verapamil and 10 microM diltiazem dilated afferent arterioles. Verapamil also elicited a modest efferent vasodilation. In the presence of either verapamil or diltiazem, the effect of ANG II to decrease efferent diameter was sustained (-15 +/- 4%); however, the effect of ANG II on afferent diameter was abolished (-1 +/- 1%). These observations document differential influences of calcium channel blockers on ANG II-mediated vasoconstriction and suggest that the pre- and postglomerular vasoconstrictor actions of ANG II may occur through different calcium entry or mobilization mechanisms.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
authors.forename: P K
authors.initials: PK
authors.lastname: Carmines
authors.forename: L G
authors.initials: LG
authors.lastname: Navar
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000502:physiology*; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012079:Renal Circulation / Q000187:drug effects*; D014661:Vasoconstriction / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D015220:Calcium Channels; D000804:Angiotensin II; D014700:Verapamil