Nonselective cation conductance activated by muscarinic and purinergic receptors in rat spiral ganglion neurons.
The present study characterizes the ionic conductances activated by acetylcholine (ACh) and ATP, two candidate neuromodulators, in isolated spiral ganglion neurons (SGNs). Brief application (1 s) of ACh evoked in a dose-dependent manner (EC(50) = 4.1 microM) a reversible inward current with a long latency (average 1.3 s), at holding potential (V(h)) = -50 mV. This current was reversibly blocked by atropine and mimicked by muscarine. Application of ATP also evoked a reversible inward current at V(h) = -50 mV, but the current showed two components. A fast component with a short latency was largely reduced when N-methyl-D-glucamine (NMDG) replaced extracellular sodium, implying a P2X-like ionotropic conductance. The second component had a longer latency (average 1.1 s) and was presumably activated by metabotropic P2Y-like receptors. The second component of ATP-evoked current shared similar characteristics with the responses evoked by ACh: the current reversed near 0 mV, displayed inward rectification, could be carried by NMDG, and was insensitive to extracellular and intracellular calcium. This ACh-/ATP-evoked conductance was reversibly inhibited by preapplication of ionomycin. These results suggest that muscarinic receptors and purinergic metabotropic receptors activate a similar large nonselective cation conductance via a common intracellular pathway in SGNs, a candidate mechanism to regulate neuronal excitability of SGNs.
Ito
Ken
K
Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, Institut National de la Santé et de la Recherche Médicale EMI 99-27, Université de Bordeaux 2, Hôpital Pellegrin, 33076 Bordeaux, France.
Dulon
Didier
D
D000109:Acetylcholine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002412:Cations / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D017136:Ion Transport / Q000502:physiology*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D009116:Muscarine / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D058914:Purinergic Antagonists; D051381:Rats; D011976:Receptors, Muscarinic / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013136:Spiral Ganglion / Q000166:cytology / Q000378:metabolism*; D013498:Suramin / Q000494:pharmacology
D002412:Cations; D002614:Chelating Agents; D007476:Ionophores; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D018722:Nicotinic Agonists; D058914:Purinergic Antagonists; D011976:Receptors, Muscarinic; D011983:Receptors, Purinergic; D004533:Egtazic Acid; D015759:Ionomycin; D013498:Suramin; D009538:Nicotine; D001285:Atropine; D009116:Muscarine; D000255:Adenosine Triphosphate; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000109:Acetylcholine; D002118:Calcium