Effect of G Protein Heterotrimer Composition on Coupling of Neurotransmitter Receptors to N-Type Ca2+Channel Modulation in Sympathetic Neurons

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-01, Vol.97 (2), p.907-912
• Main Authors: Jeong, Seong-Woo, Ikeda, Stephen R.
• Format: Article
• Language: English
• Subjects: Biological Sciences; Cell lines; Chemical composition; Complementary DNA; Neurology; Neurons; Neurotransmitter receptors; Norepinephrine; Prostaglandins; Protein subunits; Proteins; Receptors; Whooping cough
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.2.907

Voltage-dependent (VD) inhibition of N-type Ca2+channels is mediated primarily by neurotransmitter receptors that couple to pertussis toxin (PTX)-sensitive G proteins (such as Goand Gi). To date, however, the composition of heterotrimeric complexes, i.e., specific Gα β γ combinations, capable of coupling receptors to N-type Ca2+channels has not been defined. We addressed this question by heterologously expressing identified Gα β γ combinations in PTX-treated rat sympathetic neurons and testing for reconstitution of agonist-mediated VD inhibition. The heterologously expressed Gα subunits were rendered PTX-insensitive by mutating the codon specifying the ADP ribosylation site. The following results were obtained from this approach. (i) Expression of GαoA, GαoB, and Gαi2(along with Gβ1γ 2) reconstituted VD inhibition mediated by α2-adrenergic, adenosine, somatostatin, and prostaglandin E2receptors. Conversely, expression of Gαi1and Gαi3was ineffective at restoring coupling. (ii) Coupling efficiency, as determined from the magnitude of reconstituted Ca2+current inhibition, depended on both the receptor and Gα subtype. The following rank order of coupling efficiency was observed:$\text{G}\alpha _{\text{oA}}=\ \text{G}\alpha _{\text{oB}}>\text{G}\alpha _{\text{i2}}$for α2-adrenergic receptor;$\text{G}\alpha _{\text{i2}}>\text{G}\alpha _{\text{oA}}=\text{G}\alpha _{\text{oB}}$for adenosine and prostaglandin E2receptors; and$\text{G}\alpha _{\text{oB}}=\text{G}\alpha _{\text{i2}}>\text{G}\alpha _{\text{oA}}$for the somatostatin receptor. (iii) In general, varying the Gβ γ composition of GαoA-containing heterotrimers had little effect on the coupling of α2-adrenergic receptors to the VD pathway. Taken together, these results suggest that multiple, diverse Gα β γ combinations are capable of coupling neurotransmitter receptors to VD inhibition of N-type Ca2+channels. Thus, if exquisite Gα β γ -coupling specificity exists in situ, it cannot arise solely from the inherent inability of other Gα β γ combinations to form functional signaling complexes.