pH has substantial effect on many enzyme systems in cells and thus modifies many cellular processes.It is therefore important to understand how intracellular pH (pHi) is regulated and the physiological and pathophysiological consequences of a deranged pHi.It is the aim of this presentation to discuss how phi is regulated in smooth muscle and endothelial cells in the vascular wall and how pHi modifies the intercellular communication in the vascular wall.Mesenteric resistance arteries (diameter about 200 μm) from rats and mice were isolated and the tone investigated under isometric or isobaric conditions.phi and intracellular [Ca2+]i were assessed using ion-sensitive fluorescent dyes and confocal microscopy, while expression of various transporters were characterized with PCR, Western blotting and immunohistochemistry.