title: Carbon monoxide activates KCa channels in newborn arteriole smooth muscle cells by increasing apparent Ca2+ sensitivity of alpha-subunits.
abstract: Carbon monoxide (CO) is a gaseous vasodilator produced by many cell types, including endothelial and smooth muscle cells. The goal of the present study was to investigate signaling mechanisms responsible for CO activation of large-conductance Ca(2+)-activated K(+) (K(Ca)) channels in newborn porcine cerebral arteriole smooth muscle cells. In intact cells at 0 mV, CO (3 microM) or CO released from dimanganese decacarbonyl (10 microM), a novel light-activated CO donor, increased K(Ca) channel activity 4.9- or 3.5-fold, respectively. K(Ca) channel activation by CO was not blocked by 1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (25 microM), a soluble guanylyl cyclase inhibitor. In inside-out patches at 0 mV, CO shifted the Ca(2+) concentration-response curve for K(Ca) channels leftward and decreased the apparent dissociation constant for Ca(2+) from 31 to 24 microM. Western blotting data suggested that the low Ca(2+) sensitivity of newborn K(Ca) channels may be due to a reduced beta-subunit-to-alpha-subunit ratio. CO activation of K(Ca) channels was Ca(2+) dependent. CO increased open probability 3.7-fold with 10 microM free Ca(2+) at the cytosolic membrane surface but only 1.1-fold with 300 nM Ca(2+). CO left shifted the current-voltage relationship of cslo-alpha currents expressed in HEK-293 cells, increasing currents 2.2-fold at +50 mV. In summary, data suggest that in newborn arteriole smooth muscle cells, CO activates low-affinity K(Ca) channels via a direct effect on the alpha-subunit that increases apparent Ca(2+) sensitivity. The optimal tuning by CO of the micromolar Ca(2+) sensitivity of K(Ca) channels will lead to preferential activation by signaling modalities, such as Ca(2+) sparks, which elevate the subsarcolemmal Ca(2+) concentration within this range.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Xi
authors.forename: Dilyara
authors.initials: D
authors.lastname: Tcheranova
authors.forename: Helena
authors.initials: H
authors.lastname: Parfenova
authors.forename: Burton
authors.initials: B
authors.lastname: Horowitz
authors.forename: Charles W
authors.initials: CW
authors.lastname: Leffler
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Jaggar
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001160:Arterioles; D002248:Carbon Monoxide / Q000494:pharmacology*; D002536:Cerebral Arteries; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects / Q000502:physiology*; D013552:Swine
chemical_list: D024681:Potassium Channels, Calcium-Activated; D002248:Carbon Monoxide