Voltage-dependent Ca2+-channel block by openers of intermediate and small conductance Ca2+-activated K+ channels in urinary bladder smooth muscle cells

We examined effects of small and intermediate conductance Ca2+-activated K+ (SK and IK) channel openers, DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) and NS309 (3-oxime-6,7-dichloro-1H-indole-2,3-dione), on L-type Ca2+ channel current (I-Ca) that was measured in smooth muscle cells isolated from mouse urinary bladder under whole cell voltage-clamp. The I-Ca was concentration-dependently inhibited by DCEBIO and NS309; half inhibition was obtained at 71.6 and 10.61 mu M, respectively. The specificity of NS309 to the IK channel over the Ca2+ channel appears to be high and higher than that of DCEBIO. DCEBIO and even NS309 may, however, substantially block Ca2+ channels when used as SK channel openers.