Ghrelin suppresses Purkinje neuron P-type Ca2+ channels via growth hormone secretagogue type 1 a receptor, the βγ subunits of Go-protein, and protein kinase A pathway

Although ghrelin receptors have been demonstrated to be widely expressed in the central nervous system and peripheral tissues of mammals, it is still unknown whether ghrelin functions in cerebellar Purkinje neurons. In this study, we identified a novel functional role for ghrelin in modulating P-type Ca2+ channel (P-type channel) currents (I-Ba) as well as action-potential firing in rat Purkinje neurons. Our results show that ghrelin at 0.1 mu M reversibly decreased I-Ba by similar to 32.3%. This effect was growth hormone secretagogue receptor la (GHS-R1a)-dependent and was associated with a hyperpolarizing shift in the voltage-dependence of inactivation. Intracellular application of GDP-beta-S and pretreatment with pertussis toxin abolished the inhibitory effects of ghrelin. Dialysis of cells with the peptide QEHA (but not the scrambled peptide SKEE), and a selective antibody raised against the G-protein alpha(o) subunit both blocked the ghrelin-induced response. Ghrelin markedly increased protein kinase A (PKA) activity, and intracellular application of PKI 5-24 as well as pretreatment of the cells with the PICA inhibitor KT-5720 abolished ghrelin-induced I-Ba decrease, while inhibition of PKC had no such effects. At the cellular level, ghrelin induced a significant increase in action-potential firing, and blockade of GHS-R1a by BIM-28163 abolished the ghrelin-induced hyperexcitability. In summary, these results suggest that ghrelin markedly decreases IBa via the activation of GHS-R1a, which is coupled sequentially to the activities of G(o)-protein beta gamma subunits and the downstream PICA pathway. This could contribute to its physiological functions, including the spontaneous firing of action potentials in cerebellar Purkinje neurons. (C) 2014 Elsevier Inc. All rights reserved.