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Voltage‐gated ionic currents in an identified modulatory cell type controlling molluscan feeding
Author(s) -
Staras Kevin,
Győri János,
Kemenes György
Publication year - 2002
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01845.x
Subject(s) - tetraethylammonium , biophysics , patch clamp , voltage clamp , tetrodotoxin , cardiac transient outward potassium current , chemistry , membrane potential , reversal potential , 4 aminopyridine , electrophysiology , neuroscience , potassium channel , biology , potassium , organic chemistry
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 (≈ 50% block at 100 µ m ), 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, Ca 2+ ‐activated, K + channel made a contribution to the total outward current. No inwardly rectifying currents were found. Two Ca 2+ currents were characterized: (i) a transient low‐voltage (−65 ± 2 mV) activated T‐type current, which was blocked in NiCl 2 (2 m m ) and was completely inactivated at ≈ −50 mV; (ii) A sustained high voltage (−40 ± 1 mV) activated current, which was blocked in CdCl 2 (100 µ m ) but not in ω‐conotoxin GVIA (10 µ m ), ω‐agatoxin IVA (500 n m ) or nifedipine (10 µ m ). This current was enhanced in Ba 2+ 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.