title: Angiotensin II-stimulated Ca2+ entry mechanisms in afferent arterioles: role of transient receptor potential canonical channels and reverse Na+/Ca2+ exchange.
abstract: In afferent arterioles, the signaling events that lead to an increase in cytosolic Ca(2+) concentration ([Ca(2+)](i)) and initiation of vascular contraction are increasingly being delineated. We have recently studied angiotensin II (ANG II)-mediated effects on sarcoplasmic reticulum (SR) mobilization of Ca(2+) and the role of superoxide and cyclic adenosine diphosphoribose in these processes. In the current study we investigated the participation of transient receptor potential canonical channels (TRPC) and a Na(+)/Ca(2+) exchanger (NCX) in Ca(2+) entry mechanisms. Afferent arterioles, isolated with the magnetized polystyrene bead method, were loaded with fura-2 to measure [Ca(2+)](i) ratiometrically. We observed that the Ca(2+)-dependent chloride channel blocker niflumic acid (10 and 50 microM) affects neither the peak nor plateau [Ca(2+)](i) response to ANG II. Arterioles were pretreated with ryanodine (100 microM) and TMB-8 to block SR mobilization via the ryanodine receptor and inositol trisphosphate receptor, respectively. The peak [Ca(2+)](i) response to ANG II was reduced by 40%. Addition of 2-aminoethoxydiphenyl borane to block TRPC-mediated Ca(2+) entry inhibited the peak [Ca(2+)](i) ANG II response by 80% and the plateau by 74%. Flufenamic acid (FFA; 50 microM), which stimulates TRPC6, caused a sustained increase of [Ca(2+)](i) of 146 nM. This response was unaffected by diltiazem or nifedipine. KB-R7943 (at the low concentration of 10 microM) inhibits reverse (but not forward) mode NCX. KB-R7943 decreased the peak [Ca(2+)](i) response to ANG II by 48% and to FFA by 38%. We conclude that TRPC6 and reverse-mode NCX may be important Ca(2+) entry pathways in afferent arterioles.
authors.affiliation: Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. sfellner@med.unc.edu
authors.forename: Susan K
authors.initials: SK
authors.lastname: Fellner
authors.forename: William J
authors.initials: WJ
authors.lastname: Arendshorst
mesh_terms: D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D005439:Flufenamic Acid / Q000494:pharmacology; D007668:Kidney / Q000098:blood supply; D008297:Male; D008833:Microcirculation; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D009544:Niflumic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D050052:TRPC Cation Channels / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D000893:Anti-Inflammatory Agents; D019831:Sodium-Calcium Exchanger; D050052:TRPC Cation Channels; C492145:Trpc6 protein, rat; D000804:Angiotensin II; D012433:Ryanodine; D009544:Niflumic Acid; D005439:Flufenamic Acid; D013890:Thiourea; D002118:Calcium