title: Angiotensin AT(1)-receptors depolarize neonatal spinal motoneurons and other ventral horn neurons via two different conductances.
abstract: Angiotensin receptors are highly expressed in neonatal spinal cord. To identify their influence on neuronal excitability, we used patch-clamp recordings in spinal cord slices to assess responses of neonatal rat (5-12 days) ventral horn neurons to bath-applied angiotensin II (ANG II; 1 microM). In 14/34 identified motoneurons tested under current clamp, ANG II induced a slowly rising and prolonged membrane depolarization, blockable with Losartan (n = 5) and (Sar(1), Val(5), Ala(8))-ANG II (Saralasin, n = 4) but not PD123319 (1 microM each; n = 4). Under voltage clamp (V(H) -65 mV), 7/22 motoneurons displayed an ANG-II-induced tetrodotoxin-resistant inward current (-128 +/- 31 pA) with a similar time course, an associated reduction in membrane conductance and net current reversal at -98.8 +/- 3.9 mV. Losartan-sensitive ANG II responses were also evoked in 27/78 tested ventral horn "interneurons." By contrast with motoneurons, their ANG-II-induced inward current was smaller (-39.9 +/- 5.2 pA) and analysis of their I-V plots revealed three patterns. In eight cells, membrane conductance decreased with net inward current reversing at -103.8 +/- 4.1 mV. In seven cells, membrane conductance increased with net current reversing at -37.9 +/- 3.6 mV. In 12 cells, I-V lines remained parallel with no reversal within the current range tested. Intracellular dialysis with GTP-gamma-S significantly prolonged the ANG II effect in seven responsive interneurons and GDP-beta-S significantly reduced the ANG II response in four other cells. Peak inward currents were significantly reduced in all 13 responding neurons recorded in slices incubated in pertussis toxin (5 microgram/ml) for 12-18 h or in 12 neurons perfused with N-ethylmaleimide. Of 29 interneurons sensitive to pertussis toxin or N-ethylmaleimide treatment, 9 cells displayed a decrease in membrane conductance that reversed at -101.3 +/- 3.8 mV. In eight cells, membrane conductance increased and reversed at -38.7 +/- 3.4 mV. In 12 cells, the I-V lines remained parallel with no reversal within the current range tested, suggesting that both conductances are modulated by pertussis toxin-sensitive G proteins. These observations reveal a direct, G-protein-mediated depolarizing action of ANG II on neonatal rat ventral horn neurons. They also imply involvement of two distinct conductances that are differentially distributed among different cell types.
authors.affiliation: National Institute on Drug Abuse, Intramural Research Program, Baltimore, Maryland 21224, USA. moz@intra.nida.nih.gov
authors.forename: Murat
authors.initials: M
authors.lastname: Oz
authors.forename: Leo P
authors.initials: LP
authors.lastname: Renaud
mesh_terms: D000779:Anesthetics, Local / Q000494:pharmacology; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D000870:Anterior Horn Cells / Q000502:physiology*; D004594:Electrophysiology; D005033:Ethylmaleimide / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007395:Interneurons / Q000502:physiology; D007473:Ion Channels / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000819:agonists / Q000502:physiology*; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000779:Anesthetics, Local; D057911:Angiotensin Receptor Antagonists; D007473:Ion Channels; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D013779:Tetrodotoxin; D037342:Pertussis Toxin; D005033:Ethylmaleimide