Glutamate‐stimulated, astrocyte‐derived carbon monoxide production is intracellular calcium concentration‐dependent in piglets

Abstract

Glutamate‐stimulated, astrocyte‐derived carbon monoxide (CO) induces vasodilation by activating big conductance Ca2+‐activated potassium (BKCa) channels in arterial myocytes. Here, we examined the hypotheses that glutamate stimulates astrocyte‐derived CO production via heme oxygenase (HO)‐2 activation by elevating [Ca2+]i and Ca2+‐calmodulin complexes in piglets. The major findings are: (1) Exogenous glutamate stimulates Ca2+ oscillations and increases [Ca2+]i in primary‐cultured astrocytes. (2) A [Ca2+]i elevation increases CO production in astrocytes with an EC50 of 310 nM. (3) If [Ca2+]i is held constant, glutamate does not affect CO production. (4) Depleting intracellular Ca2+ stores in astrocytes with a sarco/endoplasmic reticulum Ca2+‐ATPases blocker, thapsigargin, decreases CO production, and blocks the glutamate‐induced increase in CO in astrocytes caused by glutamate and the exogenous HO substrate, hemin. (5) The calmodulin inhibitor, calmidazolium, blocks glutamate‐induced CO production in freshly isolated piglet astrocytes. Taken together, our data are consistent with the hypothesis that glutamate elevates [Ca2+]i in astrocytes, which triggers Ca2+‐calmodulin complex formation, leading to HO‐2 activation and CO production. (NIH 5R37HL042851 and 5R01HL034059).