Voltage-gated ionic currents in an identified modulatory cell type controlling molluscan feeding.
An important modulatory cell type, found in all molluscan feeding networks, was investigated using two-electrode voltage- and current-clamp methods. In the cerebral giant cells of Lymnaea, a transient inward Na+ current was identified with activation at -58 +/- 2 mV. It was sensitive to tetrodotoxin only in high concentrations (approximately 50% block at 100 microm), a characteristic of Na+ channels in many molluscan neurons. A much smaller low-threshold persistent Na+ current (activation at < -90 mV) was also identified. Two purely voltage-sensitive outward K+ currents were also found: (i) a transient A-current type which was activated at -59 +/- 4 mV and blocked by 4-aminopyridine; (ii) a sustained tetraethylammonium-sensitive delayed rectifier current which was activated at -47 +/- 2 mV. There was also evidence that a third, Ca2+-activated, K+ channel made a contribution to the total outward current. No inwardly rectifying currents were found. Two Ca2+ currents were characterized: (i) a transient low-voltage (-65 +/- 2 mV) activated T-type current, which was blocked in NiCl2 (2 mm) and was completely inactivated at approximately -50 mV; (ii) A sustained high voltage (-40 +/- 1 mV) activated current, which was blocked in CdCl2 (100 microm) but not in omega-conotoxin GVIA (10 microm), omega-agatoxin IVA (500 nm) or nifedipine (10 microm). This current was enhanced in Ba2+ saline. Current-clamp experiments revealed how these different current types could define the membrane potential and firing properties of the cerebral giant cells, which are important in shaping the wide-acting modulatory influence of this neuron on the rest of the feeding network.
Staras
Kevin
K
Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, UK.
Gyóri
János
J
Kemenes
György
G
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D019771:Axotomy; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology; D004594:Electrophysiology; D005247:Feeding Behavior / Q000502:physiology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000009:adverse effects / Q000502:physiology*; D008195:Lymnaea; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000502:physiology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007473:Ion Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D026941:Sodium Channel Blockers; D015222:Sodium Channels