Different mechanisms underlying the stimulation of KCa channels by nitric oxide and carbon monoxide

Abstract

The molecular mechanisms underlying the effects of nitric oxide (NO) and carbon monoxide (CO), individually and collectively, on large-conductance calcium-activated K + (K Ca ) channels were investigated in rat vascular smooth muscle cells (SMCs). Both NO and CO increased the activity of native K Ca channels. Dehydrosoyasaponin-I, a specific agonist for subunit of K Ca channels, increased the open probability of native K Ca channels only when it was delivered to the cytoplasmic surface of membrane. CO, but not NO, further increased the activity of native K Ca channels that had been maximally stimulated by dehydrosoyasaponin-I. After treatment of SMCs with anti-K Ca , subunit antisense oligodeoxynucleotides, the stimulatory effect of NO, but not of CO, on K Ca channels was nullified. CO, but not NO, enhanced the K Ca current densities of heterologously expressed cloned K Ca , subunit, showing that the presence of K Ca , subunit is not a necessity for the effect of CO but essential for that of NO. Finally, pretreatment of SMCs with NO abolished the effects of subsequently applied CO or diethyl pyrocarbonate on K Ca channels. In summary, the stimulatory effects of CO and NO on K Ca channels rely on the specific interactions of these gases with K Ca , and K Ca , subunits.