Differential K⁺ channel distribution in smooth muscle cells isolated from the pulmonary arterial tree of the rat

Intracellular photorelease of Ca²⁺ demonstrated the presence of Ca²⁺-activated K⁺ channels in smooth muscle cells isolated from different locations of the rat pulmonary arterial tree. However, cell-free patch studies revealed marked differences in K⁺ channel distribution. In the main pulmonary artery the most frequently observed K⁺ channel was a ˜245pS conductance Ca²⁺- and ATP-activated (K_{Ca, ATP}) channel. In small pulmonary arteries two K⁺ channel types predominated: the K_{Ca, ATP} channel and a ˜185pS conductance K⁺ channel insensitive to intracellular Ca²⁺, ATP and voltage. This difference in K⁺ channel distribution may highlight a more complex regulatory mechanism for controlling membrane potential in small pulmonary arteries, reflecting their physiologically more important role in governing pulmonary vascular reactivity.