Carbon monoxide activates KCa channels in newborn arteriole smooth muscle cells by increasing apparent Ca sensitivity of -subunits

Xi, Qi, Dilyara Tcheranova, Helena Parfenova, Burton Horowitz, Charles W. Leffler, and Jonathan H. Jaggar. Carbon monoxide activates KCa channels in newborn arteriole smooth muscle cells by increasing apparent Ca sensitivity of -subunits. Am J Physiol Heart Circ Physiol 286: H610–H618, 2004. First published October 16, 2003; 10.1152/ajpheart.00782.2003.—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 -activated K (KCa) channels in newborn porcine cerebral arteriole smooth muscle cells. In intact cells at 0 mV, CO (3 M) or CO released from dimanganese decacarbonyl (10 M), a novel light-activated CO donor, increased KCa channel activity 4.9or 3.5-fold, respectively. KCa channel activation by CO was not blocked by 1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (25 M), a soluble guanylyl cyclase inhibitor. In inside-out patches at 0 mV, CO shifted the Ca concentration-response curve for KCa channels leftward and decreased the apparent dissociation constant for Ca from 31 to 24 M. Western blotting data suggested that the low Ca sensitivity of newborn KCa channels may be due to a reduced -subunit-to-subunit ratio. CO activation of KCa channels was Ca dependent. CO increased open probability 3.7-fold with 10 M free Ca at the cytosolic membrane surface but only 1.1-fold with 300 nM Ca . CO left shifted the current-voltage relationship of cslocurrents expressed in HEK-293 cells, increasing currents 2.2fold at 50 mV. In summary, data suggest that in newborn arteriole smooth muscle cells, CO activates low-affinity KCa channels via a direct effect on the -subunit that increases apparent Ca sensitivity. The optimal tuning by CO of the micromolar Ca sensitivity of KCa channels will lead to preferential activation by signaling modalities, such as Ca sparks, which elevate the subsarcolemmal Ca concentration within this range.