Gβ2 and Gβ4 participate in the opioid and adrenergic receptor-mediated Ca²⁺ channel modulation in rat sympathetic neurons

Cardiac function is regulated in part by the sympathetic branch of the autonomic nervous system via the stellate ganglion (SG) neurons. Neurotransmitters, such as noradrenaline (NA), and neuropeptides, including nociceptin (Noc), influence the excitability of SG neurons by modulating Ca²⁺ channel function following activation of the adrenergic and nociceptin/orphanin FQ peptide (NOP) opioid receptors, respectively. The regulation of Ca²⁺ channels is mediated by Gβγ, but the specific Gβ subunit that modulates the channels is not known. In the present study, small interference RNA (siRNA) was employed to silence the natively expressed Gβ proteins in rat SG tissue and to examine the coupling specificity of adrenergic and NOP opioid receptors to Ca²⁺ channels employing the whole-cell variant of the patch-clamp technique. Western blotting analysis showed that Gβ1, Gβ2 and Gβ4 are natively expressed. The knockdown of Gβ2 or Gβ4 led to a significant decrease of the NA- and Noc-mediated Ca²⁺ current inhibition, while Gβ1 silencing was without effect. However, sustaining low levels of Gβ2 resulted in an increased expression of Gβ4 and a concomitant compensation of both adrenergic and opioid signalling pathways modulating Ca²⁺ channels. Conversely, Gβ4-directed siRNA was not accompanied with a compensation of the signalling pathway. Finally, the combined silencing of Gβ2 and Gβ4 prevented any additional compensatory mechanisms. Overall, our studies suggest that in SG neurons, Gβ2 and Gβ4 normally maintain the coupling of Ca²⁺ channels with the receptors, with the latter subtype responsible for maintaining the integrity of both pathways.