The mechanisms underlying the inhibition of CO effect on K_Ca channels by NO. The dashed lines beside each trace indicate the closed channel current level. Membrane potential, +30 mV. [Ca²⁺]_i in these experiments was 1 μM. (a) Pretreatment of the outside-out membrane patch with SNP rendered the K_Ca channels insensitive to DEPC modification. (b) Inclusion of DHS in the pipette solution increased the NP_o of the outside-out patches but did not prevent K_Ca channels from inhibition by the subsequent bath-applied DEPC. (c) Inclusion of DEPC in the pipette solution did not interfere with the excitatory effect of the bath-applied SNP on the NP_o in the inside-out patches. (d) Inclusion of DEPC in the pipette solution did not interfere with the excitatory effect of the bath-applied DHS on the NP_o in the inside-out patches. (e) The presence of SOD in the bath solution did not remove the inhibition of CO effect–by SNP.