Functional expression of inwardly rectifying and ATP-sensitive potassium channels in human pulmonary artery smooth...

The resting membrane potential (V_M) of vascular cells is a key determinant of arterial tone, integrating multiple ionic conductances to control smooth muscle contractility and endothelial signalling. In the human pulmonary circulation, the specific K⁺ channels responsible for setting the V_M of smooth muscle cells (SMCs) and endothelial cells (ECs) remain incompletely defined. This study investigated whether inwardly rectifying (Kir2) and ATP-sensitive (K_ATP) K⁺ channels are functionally expressed in native human pulmonary artery (PA) SMCs and ECs and assessed their contribution to vascular tone. Combining patch-clamp electrophysiology, immunofluorescence and wire myography, we evaluated channel expression and function in freshly isolated PASMCs and PAECs, and intact PAs. Kir2 channels were identified by Ba²⁺-sensitive inward currents with a characteristic rectification profile, supported by immunolabelling of Kir2.1 and Kir2.2 subunits. Functionally, BaCl₂ induced concentration-dependent contractions of PA rings and significantly attenuated acetylcholine-evoked, endothelium-dependent relaxation, revealing a tonic vasodilatory role for Kir2 channels. K_ATP currents, activated by pinacidil and blocked by glibenclamide and PNU-37883A, were also observed in PASMCs and PAECs, consistent with immunodetection of Kir6.1 and SUR2 subunits. In isolated PAs, pinacidil elicited concentration-dependent vasodilatation, which was significantly reduced by K_ATP channel blockade. Collectively, these findings demonstrate for the first time the functional presence of Kir2 and K_ATP channels in native human pulmonary vascular cells, and their modulatory role on V_M and arterial tone. These channels emerge as key electro-metabolic regulators of pulmonary vascular function and promising therapeutic targets in diseases characterized by V_M dysregulation, such as pulmonary arterial hypertension. KEY POINTS: Inwardly rectifying (Kir2) K⁺ channels are key regulators of the resting membrane potential (V_M) in different vascular cell types across multiple vascular beds, whereas ATP-sensitive (K_ATP) K⁺ channels detect changes in the metabolic state of vascular cells and translate these changes into V_M modulation. Despite their well-established physiological relevance, a comprehensive characterization of Kir2 and K_ATP channels in freshly isolated human pulmonary vascular cells - particularly within the endothelium - remains lacking. Our study provides compelling evidence for the functional expression of Kir2 and K_ATP channels in native human pulmonary arterial smooth muscle and endothelial cells, demonstrating their contribution to V_M regulation and pulmonary vascular tone at rest and in response to specific stimuli.