The effect of endogenous CO on whole-cell KCa currents in rat tail artery SMCs. (a) KCa currents were suppressed by Cr-MP (30 μM). The I-V relationships of the KCa channels were constructed 10 minutes before and after the application of Cr-MP. n = 7. (b) KCa currents were increased by HLL (50 μM). The I-V relationships of the KCa channels were constructed 10 minutes before and after the application of HLL. n = 6. (c) KCa 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 KCa 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.