| Abstrakt: |
The orexigenic gut peptide ghrelin is an endogenous ligand for the growth hormone secretagogue receptor type 1a (GHSR1a). Systemic ghrelin administration has previously been shown to increase gastric motility and emptying. While these effects are known to be mediated by the vagus nerve, the cellular mechanism underlying these effects remains unclear. Therefore, the purpose of the present study was to investigate the signaling mechanism by which GHSR1a inhibits voltage-gated Ca2+channels in isolated rat gastric vagal afferent neurons using whole-cell patch-clamp electrophysiology. The ghrelin pharmacological profile indicated that Ca2+currents were inhibited with a log (Ic50) = –2.10 ± 0.44 and a maximal inhibition of 42.8 ± 5.0%. Exposure to the GHSR1a receptor antagonist (D-Lys3)-GHRP-6 reduced ghrelin-mediated Ca2+channel inhibition (29.4 ± 16.7% vs. 1.9 ± 2.5%, n= 6, P= 0.0064). Interestingly, we observed that activation of GHSR1a inhibited Ca2+currents through both voltage-dependent and voltage-independent pathways. We also treated the gastric neurons with either pertussis toxin (PTX) or YM-254890 to examine whether the Ca2+current inhibition was mediated by the Gαi/oor Gαq/11family of subunits. Treatment with both PTX (Ca2+current inhibition = 15.7 ± 10.6%, n= 8, P= 0.0327) and YM-254890 (15.2 ± 11.9%, n= 8, P= 0.0269) blocked ghrelin’s effects on Ca2+currents, as compared with control neurons (34.3 ± 18.9%, n= 8). These results indicate GHSR1a can couple to both Gαi/oand Gαq/11in gastric vagal afferent neurons. Overall, our findings suggest GHSR1a-mediated inhibition of Ca2+currents occurs through two distinct pathways, offering necessary insights into the cellular mechanisms underlying ghrelin’s regulation of gastric vagal afferents. |
