Levcromakalim decreases vascular tone, cytoplasmic Ca²⁺ and Ca²⁺ sensitivity in canine basilar artery

The involvement of large conductance Ca²⁺-activated K⁺ channels (BK) and ATP-sensitive K⁺ (K(ATP)) channels in the regulation of canine basilar arterial tone was estimated in the presence of the agonist and blockers of these channels, by simultaneously measuring the changes in intracellular Ca²⁺ concentration ([Ca²⁺](i)) with the fura-2 microfluorimetric method. In the resting condition, levcromakalim reduced [Ca²⁺](i) and vascular tone. Levcromakalim suppressed the serotonin-induced increases in [Ca²⁺](i) and force of contraction, the maximum effects of which were much greater than those of nicardipine. The inhibitory effects of levcromakalim were blocked by glibenclamide but not by tetraethylammonium (TEA) or iberiotoxin (IbTX). In the presence of levcromakalim, the curve relating [Ca²⁺](i) with force in the presence of serotonin at different extracellular Ca²⁺ concentration ([Ca²⁺](o)) was shifted down- and right-ward compared with that in the absence of levcromakalim, suggesting that levcromakalim may reduce the Ca²⁺-sensitivity of the contractile proteins. Thus, levcromakalim may be a good candidate to suppress delayed cerebral vasospasm after subarachnoid hemorrhage.