title: Stress peptide PACAP engages multiple signaling pathways within the carotid body to initiate excitatory responses in respiratory and sympathetic chemosensory afferents.
abstract: Consistent with a critical role in respiratory and autonomic stress responses, the carotid bodies are strongly excited by pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide implicated in stress responses throughout the sympathetic nervous system. PACAP excites isolated carotid body glomus cells via activation of PAC1 receptors, with one study suggesting PAC1-induced excitation is due entirely to protein kinase A (PKA)-mediated inhibition of TASK channels. However, in other systems, PAC1 is known to be coupled to multiple intracellular signaling pathways, including PKA, phospholipase C (PLC), phospholipase D (PLD), and protein kinase C (PKC), that trigger multiple downstream effectors including increased Ca²⁺ mobilization, inhibition of various K⁺ channels, and activation of nonselective cation channels. This study tests if non-PKA/TASK channel signaling helps mediate the stimulatory effects of PACAP on the carotid body. Using an ex vivo arterially perfused rat carotid body preparation, we show that PACAP-38 stimulates carotid sinus nerve activity in a biphasic manner (peak response, falling to plateau). PKA blocker H-89 only reduced the plateau response (~41%), whereas the TASK-1-like K⁺ channel blocker/transient receptor potential vanilloid 1 channel agonist anandamide only inhibited the peak response (~48%), suggesting involvement of additional pathways. The PLD blocker CAY10594 significantly inhibited both peak and plateau responses. The PLC blocker U73122 decimated both peak and plateau responses. Brefeldin A, a blocker of Epac (cAMP-activated guanine exchange factor, reported to link Gs-coupled receptors with PLC/PLD), also reduced both phases of the response, as did blocking signaling downstream of PLC/PLD with the PKC inhibitors chelerythrine chloride and GF109203X. Suggesting the involvement of non-TASK ion channels in the effects of PACAP, the A-type K⁺ channel blocker 4-aminopyridine, and the putative transient receptor potential channel (TRPC)/T-type calcium channel blocker SKF96365 each significantly inhibited the peak and steady-state responses. These data suggest the stimulatory effect of PACAP-38 on carotid body sensory activity is mediated through multiple signaling pathways: the PLC-PKC pathways predominates, with TRPC and/or T-type channel activation and Kv channel inactivation; only partial involvement is attributable to PKA and PLD activation.
authors.affiliation: Department of Physiology and Pharmacology, Hotchkiss Brain Institute, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Arijit
authors.initials: A
authors.lastname: Roy
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Derakhshan
authors.forename: Richard J A
authors.initials: RJ
authors.lastname: Wilson
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002344:Carotid Body / Q000187:drug effects / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000187:drug effects; D063388:Endocannabinoids / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D008297:Male; D023421:Models, Animal; D009419:Nerve Tissue Proteins; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology / Q000502:physiology*; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D024683:Potassium Channels, Tandem Pore Domain / Q000187:drug effects / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000187:drug effects; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012143:Respiratory Physiological Phenomena / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013312:Stress, Physiological / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
chemical_list: D001095:Arachidonic Acids; D063388:Endocannabinoids; D004791:Enzyme Inhibitors; D004963:Estrenes; D009419:Nerve Tissue Proteins; D010726:Phosphodiesterase Inhibitors; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D053284:Polyunsaturated Alkamides; D024683:Potassium Channels, Tandem Pore Domain; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C420132:potassium channel subfamily K member 3; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; C078814:anandamide
keywords: PACAP; arterial chemoreceptor; carotid body; hypoxia; stress peptide