We have previously shown that pheochromocytoma (PC12) cells rapidly depolarize and undergo Ca 2+ influx through voltage-dependent Ca 2+ channels in response to moderate hypoxia and that intracellular free Ca 2+ is modulated by activation of dopamine D 2 receptors in this cell type. The present study shows that D 2 (quinpirole-mediated) inhibition of a voltage-dependent Ca 2+ current (I Ca ) in PC12 cells is dramatically attenuated after chronic exposure to moderate hypoxia (24 h at 10% O 2 ). Pretreatment of cells with pertussis toxin abolished D 2 -mediated inhibition of I Ca . The D 2 -induced inhibition of I Ca did not depend on protein kinase A (PKA), as it persisted both in the presence of a specific PKA inhibitor (PKI) and in PKA-deficient PC12 cells. Prolonged exposure to hypoxia (24 h) significantly reduced the level of G i/o α immunoreactivity, but did not alter Gβ levels. Furthermore, dialysis of recombinant G o α protein through the patch pipette restored the inhibitory effect of quinpirole in cells chronically exposed to hypoxia. We conclude that the attenuation of the D 2 -mediated inhibition of I Ca by chronic hypoxia is caused by impaired receptor-G protein coupling, due to reduced levels of G o α protein. This attenuated feedback modulation of I Ca by dopamine may allow for a more sustained Ca 2+ influx and enhanced cellular excitation during prolonged hypoxia.