What's where and why at a vascular myoendothelial microdomain signalling complex.

1. Modulation of vascular cell calcium is critical for the control of vascular tone, blood flow and pressure. 2. Specialized microdomain signalling sites associated with calcium modulation are present in vascular smooth muscle cells, where spatially localized channels and calcium store receptors interact functionally. Anatomical studies suggest that such sites are also present in endothelial cells. 3. The characteristics of these sites near heterocellular myoendothelial gap junctions (MEGJs) are described, focusing on rat mesenteric artery. The MEGJs enable current and small molecule transfer to coordinate arterial function and are thus critical for endothelium-derived hyperpolarization, regulation of smooth muscle cell diameter in response to contractile stimuli and vasomotor conduction over distance. 4. Although MEGJs occur on endothelial cell projections within internal elastic lamina (IEL) holes, not all IEL holes have MEGJ-related projections (approximately 0-50% of such holes have MEGJ-related projections, with variations occurring within and between vessels, species, strains and disease). 5. In rat mesenteric, saphenous and caudal cerebellar artery and hamster cheek pouch arteriole, but not rat middle cerebral artery or cremaster arteriole, intermediate conductance calcium-activated potassium channels (IK(Ca)) localize to endothelial cell projections. 6. Rat mesenteric artery MEGJ connexins and IK(Ca) are in close spatial association with endothelial cell inositol 1,4,5-trisphosphate receptors and endoplasmic reticulum. 7. Data suggest a relationship between spatially associated endothelial cell ion channels and calcium stores in modulation of calcium release and action. Differences in spatial relationships between ion channels and calcium stores in different vessels reflect heterogeneity in vasomotor function, representing a selective target for the control of endothelial and vascular function.