Mechanisms underlying selective coupling of endothelial Ca²⁺ signals with eNOS vs. IK/SK channels in systemic and pulmonary arteries

Key points: Endothelial cell TRPV4 (TRPV4_EC ) channels exert a dilatory effect on the resting diameter of resistance mesenteric and pulmonary arteries. Functional intermediate- and small-conductance K⁺ (IK and SK) channels and endothelial nitric oxide synthase (eNOS) are present in the endothelium of mesenteric and pulmonary arteries. TRPV4_EC sparklets preferentially couple with IK/SK channels in mesenteric arteries and with eNOS in pulmonary arteries. TRPV4_EC channels co-localize with IK/SK channels in mesenteric arteries but not in pulmonary arteries, which may explain TRPV4_EC -IK/SK channel coupling in mesenteric arteries and its absence in pulmonary arteries. The presence of the nitric oxide-scavenging protein, haemoglobin α, limits TRPV4_EC -eNOS signalling in mesenteric arteries. Spatial proximity of TRPV4_EC channels with eNOS and the absence of haemoglobin α favour TRPV4_EC -eNOS signalling in pulmonary arteries.

Abstract: Spatially localized Ca²⁺ signals activate Ca²⁺ -sensitive intermediate- and small-conductance K⁺ (IK and SK) channels in some vascular beds and endothelial nitric oxide synthase (eNOS) in others. The present study aimed to uncover the signalling organization that determines selective Ca²⁺ signal to vasodilatory target coupling in the endothelium. Resistance-sized mesenteric arteries (MAs) and pulmonary arteries (PAs) were used as prototypes for arteries with predominantly IK/SK channel- and eNOS-dependent vasodilatation, respectively. Ca²⁺ influx signals through endothelial transient receptor potential vanilloid 4 (TRPV4_EC ) channels played an important role in controlling the baseline diameter of both MAs and PAs. TRPV4_EC channel activity was similar in MAs and PAs. However, the TRPV4 channel agonist GSK1016790A (10 nm) selectively activated IK/SK channels in MAs and eNOS in PAs, revealing preferential TRPV4_EC -IK/SK channel coupling in MAs and TRPV4_EC -eNOS coupling in PAs. IK/SK channels co-localized with TRPV4_EC channels at myoendothelial projections (MEPs) in MAs, although they lacked the spatial proximity necessary for their activation by TRPV4_EC channels in PAs. Additionally, the presence of the NO scavenging protein haemoglobin α (Hbα) within nanometer proximity to eNOS limits TRPV4_EC -eNOS signalling in MAs. By contrast, co-localization of TRPV4_EC channels and eNOS at MEPs, and the absence of Hbα, favour TRPV4_EC -eNOS coupling in PAs. Thus, our results reveal that differential spatial organization of signalling elements determines TRPV4_EC -IK/SK vs. TRPV4_EC -eNOS coupling in resistance arteries.