It is generally accepted that relatively mild hypoxia inhibits mitochondrial oxidative phosphorylation in O2-sensing cells, and thereby mediates, in part, cell activation. However, the mechanism by which this process is coupled to discrete, cell-specific Ca2+ signalling mechanisms remains elusive. We considered the possibility that hypoxia may increase the cellular ATP/AMP ratio, increase the activity of AMP-activated protein kinase (AMPK) and thereby evoke Ca2+ signals in O2-sensing cells. C...