The goal of the present study was to test the hypothesis that local Ca²⁺ release events (Ca²⁺ sparks) deliver high local Ca²⁺concentration to activate nearby Ca²⁺-sensitive K⁺ (BK) channels in the cell membrane of arterial smooth muscle cells. Ca²⁺ 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 Ca²⁺ of 19 μM and a Hill coefficient of 2.9 at −40 mV. At near-physiological intracellular Ca²⁺ concentration ([Ca²⁺]_i; 100 nM) and membrane potential (−40 mV), the open probability of a single BK channel was low (1.2 × 10⁻⁶). A Ca²⁺spark increased BK channel activity to 18. Assuming that 1–100% of the BK channels are activated by a single Ca²⁺ spark, BK channel activity increases 6 × 10⁵-fold to 6 × 10³-fold, which corresponds to ∼30 μM to 4 μM spark Ca²⁺ concentration. 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca²⁺sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca²⁺ spark sites are in close proximity to the BK channels and that local [Ca²⁺]_i reaches micromolar levels to activate BK channels.