Micromolar Ca(2+) from sparks activates Ca(2+)-sensitive K(+) channels in rat cerebral artery smooth muscle.
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.
Pérez
G J
GJ
Department of Pharmacology, University of Vermont, Burlington, Vermont 05405, USA.
Bonev
A D
AD
Nelson
M T
MT
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002536:Cerebral Arteries; D002614:Chelating Agents / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D005260:Female; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008297:Male; D018613:Microscopy, Confocal; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D051381:Rats; D017207:Rats, Sprague-Dawley
D002614:Chelating Agents; D051036:Large-Conductance Calcium-Activated Potassium Channels; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D002118:Calcium