Presynaptic modulation of rat arterial chemoreceptor function by 5-HT: role of K+ channel inhibition via protein kinase C.
The peripheral control of breathing is mediated by O2-sensitive carotid body (CB) type 1 cells, which express multiple neurotransmitters including the monoamines, dopamine and serotonin (5-HT). Whereas dopamine has been extensively studied, 5-HT has received little attention. Here, to elucidate the role of 5-HT in CB chemotransmission, we used perforated-patch recording from rat type 1 cell clusters and co-cultured petrosal (afferent) neurones. 5-HT induced action potentials and/or membrane depolarization associated with a conductance decrease in approximately 40% of recordings from type 1 cells (n = 78/192). These responses were markedly inhibited by the 5-HT2 receptor antagonist ketanserin (10-50 microM) and by the protein kinase C (PKC) inhibitor chelerythrine (50 microM). The PKC activator 1-oleoyl-2-acetylglycerol (OAG; 50 microM) mimicked the 5-HT-induced depolarization, and the combined effects of 5-HT and OAG were non-additive. The 5-HT-induced responses reversed near the potassium (K+) equilibrium potential (at approximately -82 mV; EK = -83 mV), suggesting inhibition of a resting K+ conductance. In type 1 cells (n = 7), voltage-activated outward K+ current was also inhibited by 1-50 microM 5-HT, an effect that was prevented by PKC inhibitors (chelerythrine and NPC 15437) and mimicked by OAG; the outward K+ current inhibited by 5-HT appeared to be predominantly a Ca(2+)-dependent K+ current. The 5-HT2 receptor blockers ketanserin and ritanserin reversibly inhibited spontaneous action potentials and the hypoxia-induced receptor potential recorded from clustered type 1 cells. Moreover, these blockers reversibly inhibited the hypoxic chemosensory response recorded postsynaptically in petrosal neurones that functionally innervated type 1 clusters in co-culture. RT-PCR and confocal immunofluorescence techniques revealed 5-HT2a receptor expression in rat CB type 1 cells. These results suggest that release of endogenous 5-HT regulates CB chemoreceptor function presynaptically, by a positive feedback mechanism involving autocrine-paracrine stimulation of 5-HT2a receptors and PKC modulation of resting and Ca(2+)-dependent K+ conductances.
Zhang
Min
M
Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1.
Fearon
Ian M
IM
Zhong
Huijun
H
Nurse
Colin A
CA
D000818:Animals; D019898:Autocrine Communication / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002344:Carotid Body / Q000166:cytology / Q000502:physiology*; D002478:Cells, Cultured; D002628:Chemoreceptor Cells / Q000166:cytology / Q000502:physiology*; D018920:Coculture Techniques; D025461:Feedback, Physiological / Q000502:physiology; D015870:Gene Expression; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019899:Paracrine Communication / Q000502:physiology; D015221:Potassium Channels / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A / Q000235:genetics / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*
D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D044402:Receptor, Serotonin, 5-HT2A; D012701:Serotonin; D011493:Protein Kinase C; D002118:Calcium