Figure 6. Schematic depiction of the subunit composition of the K_ATP and maxi-K channels (K_Ca) in corporal smooth muscle. (Panel A): As illustrated, the , or pore-forming component of the K_ATP channel, is a tetramer of homomeric subunits (stippled; Kir; inward rectifier). The subunits are associated in a 1:1 stoichiometry with homomeric ß subunits (sulfonylurea receptors, SUR; dark semicircles). (Panel B): As illustrated, the , or pore-forming component of the maxi-K channel, is a tetramer of homomeric subunits (gray). The subunits are associated in a 1:1 stoichiometry with homomeric ß subunits (dark ovals).