title: The oxytocin-induced inward current in vagal neurons of the rat is mediated by G protein activation but not by an increase in the intracellular calcium concentration.
abstract: The neuropeptide oxytocin can depolarize parasympathetic preganglionic neurons in the dorsal motor nucleus of the vagus nerve of the rat by generating a sustained inward current, which is sodium-dependent and tetrodotoxin-insensitive. The second messenger activated by oxytocin receptor binding is, however, not yet known. In the present study, we attempted to characterize it by using the whole-cell recording technique and brainstem slices. When loaded with GTP-gamma-S, a non-hydrolysable analogue of GTP, vagal neurons generated a persistent inward current in the absence of agonist and the oxytocin effect was suppressed, suggesting that the peptide-evoked current was mediated by G-protein activation. Loading vagal neurons with the calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N',-tetraacetic acid (BAPTA) suppressed a calcium-dependent, slowly decaying potassium aftercurrent but did not affect the oxytocin response, suggesting that the latter was not mediated by an agonist-induced increase in the intracellular calcium concentration. Protein kinase C (PKC) activation was probably not involved, since the peptide-evoked current was not modified by loading neurons with the PKC inhibitor H7. Thus, the oxytocin-evoked current in vagal neurons was probably not mediated by phospholipase C-beta (PLC-beta) activation. Loading neurons with 8-Br-cAMP or with an adenylyl cyclase activator (forskolin) reduced the oxytocin-evoked current by about half. SQ 22536, an adenylyl cyclase inhibitor, reduced this current by a similar amount. However, the peptide-evoked current was unaffected by Rp-cAMPS and Sp-cAMPS, an inhibitor and an activator, respectively, of cAMP-dependent protein kinase (PKA). We suggest that oxytocin activates two distinct signalling pathways in vagal neurons: one which is cAMP-dependent, but PKA-independent, and one, unidentified, which is PLC-beta-and cAMP-independent. Each pathway accounts for about half of the peptide effect and both appear to involve G-protein activation.
authors.affiliation: Department of Physiology, University Medical Centre, Geneva, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Alberi
authors.forename: J J
authors.initials: JJ
authors.lastname: Dreifuss
authors.forename: M
authors.initials: M
authors.lastname: Raggenbass
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001933:Brain Stem / Q000166:cytology; D002021:Buffers; D002118:Calcium / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D010121:Oxytocin / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013873:Thionucleotides / Q000494:pharmacology; D014630:Vagus Nerve / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D002021:Buffers; D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D013873:Thionucleotides; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016957:adenosine-3',5'-cyclic phosphorothioate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D010121:Oxytocin; D016202:N-Methylaspartate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D002118:Calcium