title: Renovascular BK(Ca) channels are not activated in vivo under resting conditions and during agonist stimulation.
abstract: We investigated the role of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels for the basal renal vascular tone in vivo. Furthermore, the possible buffering by BK(Ca) of the vasoconstriction elicited by angiotensin II (ANG II) or norepinephrine (NE) was investigated. The possible activation of renal vascular BK(Ca) channels by cAMP was investigated by infusing forskolin. Renal blood flow (RBF) was measured in vivo using electromagnetic flowmetry or ultrasonic Doppler. Renal preinfusion of tetraethylammonium (TEA; 3.0 mumol/min) caused a small reduction of baseline RBF, but iberiotoxin (IBT; 0.3 nmol/min) did not have any effect. Renal injection of ANG II (1-4 ng) or NE (10-40 ng) produced a transient decrease in RBF. These responses were not affected by preinfusion of TEA or IBT. Renal infusion of the BK(Ca) opener NS-1619 (90.0 nmol/min) did not affect basal RBF or the response to NE, but it attenuated the response to ANG II. Coadministration of NS-1619 with TEA or IBT abolished this effect. Forskolin caused renal vasodilation that was not inhibited by IBT. The presence of BK(Ca) channels in the preglomerular vessels was confirmed by immunohistochemistry. Despite their presence, there is no indication for a major role for BK(Ca) channels in the control of basal renal tone in vivo. Furthermore, BK(Ca) channels do not have a buffering effect on the rat renal vascular responses to ANG II and NE. The fact that NS-1619 attenuates the ANG II response indicates that the renal vascular BK(Ca) channels can be activated under certain conditions.
authors.affiliation: Division of Renal and Cardiovascular Research, Department of Medical Physiology, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Linda
authors.initials: L
authors.lastname: Magnusson
authors.forename: Charlotte Mehlin
authors.initials: CM
authors.lastname: Sorensen
authors.forename: Thomas Hartig
authors.initials: TH
authors.lastname: Braunstein
authors.forename: Niels-Henrik
authors.initials: NH
authors.lastname: Holstein-Rathlou
authors.forename: Max
authors.initials: M
authors.lastname: Salomonsson
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D004574:Electromagnetic Fields; D007150:Immunohistochemistry; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000378:metabolism*; D008297:Male; D009129:Muscle Tonus / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects / Q000502:physiology*; D012212:Rheology; D013268:Stimulation, Chemical; D019789:Tetraethylammonium / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001562:Benzimidazoles; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D026902:Potassium Channel Blockers; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; C086491:NS 1619; D005576:Colforsin; D019789:Tetraethylammonium; C064719:iberiotoxin; D009638:Norepinephrine