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Micromolar Ca(2+) from sparks activates Ca(2+)-sensitive K(+) channels in rat cerebral artery smooth muscle.
PĂ©rez G, Bonev A, Nelson MT
American Journal of Physiology-Cell Physiology. 2001;281( 6):C1769-75.
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Abstract
The goal of the present study was to test the hypothesis that local Ca(2+) release events (Ca(2+) sparks) deliver high local Ca(2+) concentration to activate nearby Ca(2+)-sensitive K(+) (BK) channels in the cell membrane of arterial smooth muscle cells. Ca(2+) sparks and BK channels were examined in isolated myocytes from rat cerebral arteries with laser scanning confocal microscopy and patch-clamp techniques. BK channels had an apparent dissociation constant for Ca(2+) of 19 microM and a Hill coefficient of 2.9 at -40 mV. At near-physiological intracellular Ca(2+) concentration ([Ca(2+)](i); 100 nM) and membrane potential (-40 mV), the open probability of a single BK channel was low (1.2 x 10(-6)). A Ca(2+) spark increased BK channel activity to 18. Assuming that 1-100% of the BK channels are activated by a single Ca(2+) spark, BK channel activity increases 6 x 10(5)-fold to 6 x 10(3)-fold, which corresponds to approximately 30 microM to 4 microM spark Ca(2+) concentration. 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca(2+) sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca(2+) spark sites are in close proximity to the BK channels and that local [Ca(2+)](i) reaches micromolar levels to activate BK channels.
Keyword(s)
Animals; Cerebral Arteries; Female; Large-Conductance Calcium-Activated Potassium Channels; Male; Microscopy, Confocal; Patch-Clamp Techniques; Potassium Channels, Calcium-Activated; Rats; Rats, Sprague-Dawley; analogs & derivatives: Egtazic Acid; cytology: Muscle, Smooth, Vascular; metabolism: Calcium; metabolism: Chelating Agents; metabolism: Potassium Channels; physiology: Calcium Signaling