Ca2+ and Mg-ATP activated potassium channels from rat pulmonary artery

We have observed a novel class of calcium-activated potassium channel which is activated by physiological levels of intracellular ATP. These KCa,ATP channels are found on smooth muscle cells isolated from the pulmonary artery. Since their activation by ATP is Mg2+ dependent and is poorly evoked by non- or slowly-hydrolyzed ATP analogues, we conclude that it involves phosphorylation. We suggest that in hypoxia a reduction of intracellular ATP may reduce KCa,ATP channel activity and thereby tend to depolarize the cells. This effect would increase Ca2+ entry through voltage-activated Ca2+ channels and contribute to vasoconstriction.