Fig. 4.

Original recordings illustrating the inhibitory effect of forskolin on the contractility of UBSM strips isolated from WT and BK-KO mice. Forskolin (30 nM–10 μM) inhibited in a concentration-dependent manner both phasic and tonic contractions of WT UBSM strips (top trace), WT UBSM strips pretreated with the BK channel inhibitor IBTX (200 nM; middle trace), and KO UBSM strips (bottom trace). The overall contractility was increased in the presence of IBTX and in the absence of functional BK channel (KO mice). Note that forskolin was less effective when the BK channel was inhibited with IBTX but had similar potency in the KO compared with WT mice. Phasic and tonic contractions were induced by addition of 1 μM carbachol in the bath solution. Dotted lines indicate the initial baseline level, which corresponds to the muscle tone.