The effect of endogenous CO on whole-cell K_Ca currents in rat tail artery SMCs. (a) K_Ca currents were suppressed by Cr-MP (30 μM). The I-V relationships of the K_Ca channels were constructed 10 minutes before and after the application of Cr-MP. n = 7. (b) K_Ca currents were increased by HLL (50 μM). The I-V relationships of the K_Ca channels were constructed 10 minutes before and after the application of HLL. n = 6. (c) K_Ca currents were not affected by treatment with biliverdin or L-lysine for 10 minutes. n = 6 in each group. In the presence of deferoxamine (DFX), HLL still increased K_Ca channel currents. Holding potential, –80 mV; test potential, +40 mV. *P < 0.05 vs. control. Data of each group in this figure were pooled from at least two batches of cells. I, current; V, membrane potential.