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

Key point Sympathetic stellate ganglion (SG) neurons that innervate cardiac muscle play an important role in regulating heart rate and contractility., In this study, we examined which Gβ protein subunit couples Ca²⁺ channels to opioid and adrenergic receptors expressed in SG neurons., We show that Gβ2 and Gβ4 are important signalling elements that maintain the transduction pathway of both receptor subtypes and Ca²⁺ channels, and how their expression levels are differentially compensated., Our results also indicate that Gβ1 subunits do not appear to play a role in either signalling pathway., The elucidation of specific G proteins that couple Ca²⁺ channels with opioid and adrenergic receptors will help us better understand how these receptors regulate synaptic transmission of SG neurons that innervate cardiac muscle., Abstract 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. [ABSTRACT FROM AUTHOR]