AMP‐activated protein kinase phosphorylation of endothelial NO synthase

TLDR

AMPK is activated by vigorous exercise and ischemic stress in rat skeletal and cardiac muscle, where it phosphorylates acetyl‑CoA carboxylase to promote fatty‑acid oxidation. AMPK associates with cardiac eNOS and phosphorylates Ser‑1177 in a Ca²⁺‑calmodulin–dependent manner to activate eNOS during ischemia, while Ca²⁺‑independent Thr‑495 phosphorylation inhibits eNOS but remains unchanged during ischemia, linking metabolic stress to cardiovascular function.

Abstract

The AMP‐activated protein kinase (AMPK) in rat skeletal and cardiac muscle is activated by vigorous exercise and ischaemic stress. Under these conditions AMPK phosphorylates and inhibits acetyl‐coenzyme A carboxylase causing increased oxidation of fatty acids. Here we show that AMPK co‐immunoprecipitates with cardiac endothelial NO synthase (eNOS) and phosphorylates Ser‐1177 in the presence of Ca 2+ ‐calmodulin (CaM) to activate eNOS both in vitro and during ischaemia in rat hearts. In the absence of Ca 2+ ‐calmodulin, AMPK also phosphorylates eNOS at Thr‐495 in the CaM‐binding sequence, resulting in inhibition of eNOS activity but Thr‐495 phosphorylation is unchanged during ischaemia. Phosphorylation of eNOS by the AMPK in endothelial cells and myocytes provides a further regulatory link between metabolic stress and cardiovascular function.