L-type calcium channel as a cardiac oxygen sensor.

Acute oxygen sensing in the heart is thought to occur through redox regulation and phosphorylation of membrane channels. Here we report a novel O2-sensing mechanism involving the C-terminus of the L-type Ca2+ channel and regulated by PKA phosphorylation. In patch-clamped myocytes, oxygen deprivation decreased ICa within 40 s. The suppressive effect of anoxia was relieved by PKA-mediated phosphorylation only when Ca2+ was the charge carrier, whereas phosphorylated IBa remained sensitive to O2 withdrawal. Suppression of Ca2+ release by thapsigargin did not alter the response of ICa to anoxia, suggesting a mandatory role for Ca2+ influx and not Ca2+-induced Ca2+ release (CICR) in O2 regulation of the channel. Consistent with this idea, mutation of 80 amino acids in the Ca2+/CaM-binding domain of the recombinant alpha1C subunit that removes Ca2+ dependent inactivation (CDI) abolished O2 sensitivity of the channel. Our findings suggest that the Ca2+/CaM binding domain of the L-type Ca2+ may represent a molecular site for O2 sensing of the heart.