title: Response of isolated rat descending vasa recta to bradykinin.
abstract: Outer medullary descending vasa recta (OMDVR) were dissected from the outer medullary vascular bundles of young rats, perfused in vitro, and loaded with fura 2 for measurement of intracellular calcium concentration ([Ca2+]i) by fluorescent ratio imaging. Fluorescent video images revealed that fura 2 selectively loads into endothelial cells but not pericytes. Bradykinin (BK), at concentrations > 10(-11) M, elicited an increase in [Ca2+]i from baseline values in the range from 50 to 100 nM to peak values of 600-800 nM followed by a sustained plateau of 150-250 nM. The vasopressin V1-receptor agonist [Phe2,Ile3,Orn8]vasopressin constricted OMDVR but yielded no observable [Ca2+]i response, a finding that is consistent with an endothelial cell origin for the fura 2 fluorescent signal. The BK [Ca2+]i response was blocked by the selective BK B2-receptor antagonists D-Arg-[Hyp3,Thi5.8,D-Phe7]BK and D-Arg-[Hyp3,D-Phe7,Leu8]BK but not the B1 antagonist des-Arg9-[Leu8]BK. BK vasodilated microperfused OMDVR that had been preconstricted with 10(-8) M angiotensin II. We conclude that the [Ca2+]i response of OMDVR endothelia can be selectively studied with fura 2, that BK increases endothelial [Ca2+]i via the B2 receptor, and that BK can vasodilate descending vasa recta.
authors.affiliation: Division of Nephrology, University of Maryland School of Medicine, Baltimore, Maryland 21201-1595, USA. tpallone@umppa1.ab.umd.edu
authors.forename: T L
authors.initials: TL
authors.lastname: Pallone
authors.forename: E P
authors.initials: EP
authors.lastname: Silldorff
authors.forename: J Y
authors.initials: JY
authors.lastname: Cheung
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000187:drug effects*; D001920:Bradykinin / Q000494:pharmacology*; D065168:Bradykinin Receptor Antagonists; D002118:Calcium / Q000378:metabolism; D004727:Endothelium / Q000378:metabolism; D066298:In Vitro Techniques; D007609:Kallidin / Q000494:pharmacology; D007679:Kidney Medulla / Q000098:blood supply*; D009130:Muscle, Smooth / Q000378:metabolism; D051381:Rats; D018002:Receptors, Bradykinin / Q000502:physiology; D017483:Receptors, Vasopressin / Q000819:agonists; D014666:Vasomotor System / Q000187:drug effects
chemical_list: D065168:Bradykinin Receptor Antagonists; D018002:Receptors, Bradykinin; D017483:Receptors, Vasopressin; D000804:Angiotensin II; D007609:Kallidin; D001920:Bradykinin; D002118:Calcium