Role of the D2 dopamine receptor in molecular adaptation to chronic hypoxia in PC12 cells

1432-2013

Calcium current Dopamine receptor G protein Hypoxia Pertussin toxin Quinpirole

Springer Online Journal Archives 1860-2000

Medicine

Abstract. We have previously shown that pheochromocytoma (PC12) cells rapidly depolarize and undergo Ca2+ influx through voltage-dependent Ca2+ channels in response to moderate hypoxia and that intracellular free Ca2+ is modulated by activation of dopamine D2 receptors in this cell type. The present study shows that D2 (quinpirole-mediated) inhibition of a voltage-dependent Ca2+ current (I Ca) in PC12 cells is dramatically attenuated after chronic exposure to moderate hypoxia (24 h at 10% O2). Pretreatment of cells with pertussis toxin abolished D2-mediated inhibition of I Ca. The D2-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 Gi/oα immunoreactivity, but did not alter Gβ levels. Furthermore, dialysis of recombinant Goα protein through the patch pipette restored the inhibitory effect of quinpirole in cells chronically exposed to hypoxia. We conclude that the attenuation of the D2-mediated inhibition of I Ca by chronic hypoxia is caused by impaired receptor–G protein coupling, due to reduced levels of Goα protein. This attenuated feedback modulation of I Ca by dopamine may allow for a more sustained Ca2+ influx and enhanced cellular excitation during prolonged hypoxia.

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