Na+, HCO3--cotransporter NBCn1 increases pHi gradients, filopodia, and migration of smooth muscle cells and promotes arterial remodelling

Aims Arterial remodelling can cause luminal narrowing and obstruct blood flow. We tested the hypothesis that cellular acidbase transport facilitates proliferation and migration of vascular smooth muscle cells (VSMCs) and enhances remodelling of conduit arteries. Methods and results Na+, HCO3--cotransport via NBCn1 (Slc4a7) mediates net acid extrusion and controls steady-state intracellular pH (pH(i)) in VSMCs of mouse carotid arteries and primary aortic explants. Carotid arteries undergo hypertrophic inward remodelling in response to partial or complete ligation in vivo, but the increase in media area and thickness and reduction in lumen diameter are attenuated in arteries from NBCn1 knock-out compared with wild-type mice. With CO2/HCO3- present, gradients for pH(i) (similar to 0.2 units magnitude) exist along the axis of VSMC migration in primary explants from wild-type but not NBCn1 knock-out mice. Knock-out or pharmacological inhibition of NBCn1 also reduces filopodia and lowers initial rates of VSMC migration after scratch-wound infliction. Interventions to reduce H+-buffer mobility (omission of CO2/HCO3- or inhibition of carbonic anhydrases) re-establish axial pHi gradients, filopodia, and migration rates in explants from NBCn1 knock-out mice. The omission of CO2/HCO3- also lowers global pHi and inhibits proliferation in primary explants. Conclusion Under physiological conditions (i.e. with CO2/HCO3- present), NBCn1-mediated HCO3- uptake raises VSMC pHi and promotes filopodia, VSMC migration, and hypertrophic inward remodelling. We propose that axial pHi gradients enhance VSMC migration whereas global acidification inhibits VSMC proliferation and media hypertrophy after carotid artery ligation. These findings support a key role of acid-base transport, particularly via NBCn1, for development of occlusive artery disease.