Inhibition of Human CaV2.3 Channels via μ-, δ- and κ-Opioid Receptor Activation

Abstract

Neuronal voltage-gated Cav2.3 channels are widely expressed in the central and peripheral nervous system where they contribute to neurotransmission and pain sensation. However, modulation of the Cav2.3 channel through G protein-coupled (GPC) μ- and δ-opioid receptors is poorly defined and has not previously been reported for κ-opioid receptors. We hypothesized that activation of human μ-, δ- or κ-opioid receptors modulates Cav2.3 channels via G protein signaling. Whole-cell Ba2+ currents were recorded in HEK293T cells co-expressing human Cav2.2 or Cav2.3 channels and μ-, δ- or κ-opioid receptors. Selective opioid receptor agonists and antagonists were used to study receptor modulation. The involvement of intracellular signaling pathways was investigated using specific inhibitors of GPC receptor-G protein coupling. Activation of μ-, δ- or κ-opioid receptors inhibited Cav2.3 and Cav2.2 channel current amplitude by ∼45% and ∼60%, respectively. Inhibition of Cav2.3 was not dependent on the type of subunit co-expressed. Inhibition of the Cav2.3 channel was primarily voltage independent, as depolarizing prepulses could not relieve the inhibited current. This was in marked contrast with the primarily voltage-dependent modulation of Cav2.2 channels that showed nearly complete recovery of the inhibited current with depolarizing prepulses. For all three types of opioid receptors, the pathway leading to Cav2.3 channel inhibition was sensitive to pertussis toxin and intracellular application of GDP-β-S. Similarly, the overexpression of a G protein subunit scavenger, myristoylated-phosducin, significantly reduced the magnitude of Cav2.3 channel inhibition. Here we demonstrate that Cav2.3 channels are efficiently inhibited by activation of μ-, δ- or κ-opioid receptors. Inhibition occurs via voltage-independent G protein signaling mechanisms. These results suggest opioid receptor controls specific members of the Cav2 channel family via differential signaling pathways. Neuronal Cav2.3 channels are therefore potential targets for opioid analgesics.