title: Superoxide enhances Ca2+ entry through L-type channels in the renal afferent arteriole.
abstract: Reactive oxygen species regulate cardiovascular and renal function in health and disease. Superoxide participates in acute calcium signaling in afferent arterioles and renal vasoconstriction produced by angiotensin II, endothelin, thromboxane, and pressure-induced myogenic tone. Known mechanisms by which superoxide acts include quenching of nitric oxide and increased ADP ribosyl cyclase/ryanodine-mediated calcium mobilization. The effect(s) of superoxide on other calcium signaling pathways in the renal microcirculation is poorly understood. The present experiments examined the acute effect of superoxide generated by paraquat on calcium entry pathways in isolated rat afferent arterioles. The peak increase in cytosolic calcium concentration caused by KCl (40 mmol/L) was 99±14 nmol/L. The response to this membrane depolarization was mediated exclusively by L-type channels because it was abolished by nifedipine but was unaffected by the T-type channel blocker mibefradil. Paraquat increased superoxide production (dihydroethidium fluorescence), tripled the peak response to KCl to 314±68 nmol/L (P<0.001) and doubled the plateau response. These effects were abolished by tempol and nitroblue tetrazolium, but not by catalase, confirming actions of superoxide and not of hydrogen peroxide. Unaffected by paraquat and superoxide was calcium entry through store-operated calcium channels activated by thapsigargin-induced calcium depletion of sarcoplasmic reticular stores. Also unresponsive to paraquat was ryanodine receptor-mediated calcium-induced calcium release from the sarcoplasmic reticulum. Our results provide new evidence that superoxide enhances calcium entry through L-type channels activated by membrane depolarization in rat cortical afferent arterioles, without affecting calcium entry through store-operated entry or ryanodine receptor-mediated calcium mobilization.
authors.affiliation: From the Department of Cell Biology and Physiology, School of Medicine, University of North Carolina at Chapel Hill.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Vogel
authors.affiliation: From the Department of Cell Biology and Physiology, School of Medicine, University of North Carolina at Chapel Hill.
authors.forename: Xi
authors.initials: X
authors.lastname: Yang
authors.affiliation: From the Department of Cell Biology and Physiology, School of Medicine, University of North Carolina at Chapel Hill.
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Moss
authors.affiliation: From the Department of Cell Biology and Physiology, School of Medicine, University of North Carolina at Chapel Hill. arends@med.unc.edu.
authors.forename: William J
authors.initials: WJ
authors.lastname: Arendshorst
mesh_terms: D000818:Animals; D001160:Arterioles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D006973:Hypertension / Q000378:metabolism / Q000503:physiopathology; D007668:Kidney / Q000098:blood supply*; D008297:Male; D008833:Microcirculation / Q000187:drug effects / Q000502:physiology; D023421:Models, Animal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010269:Paraquat / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D017382:Reactive Oxygen Species; D013481:Superoxides; D011189:Potassium Chloride; D010269:Paraquat; D002118:Calcium
keywords: calcium signaling; hypertension; nephrology; reactive oxygen species; superoxides