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Neurotransmitters decrease the calcium conductance activated by depolarization of embryonic chick sensory neurones.
Author(s) -
Dunlap K,
Fischbach G D
Publication year - 1981
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1981.sp013841
Subject(s) - depolarization , biophysics , chemistry , membrane potential , conductance , dorsal root ganglion , reversal potential , calcium , voltage dependent calcium channel , electrophysiology , neuroscience , serotonin , patch clamp , sensory system , biology , biochemistry , receptor , physics , organic chemistry , condensed matter physics
Several neurotransmitters including noradrenaline (NA), gamma‐aminobutyric acid (GABA) and serotonin (5‐HT), and also certain peptides, decrease the duration of the Na+‐Ca2+ action potential recorded in cell bodies of embryonic chick dorsal root ganglion neurones maintained in cell culture. To determine if these agents decreased action potential duration by affecting Ca2+ channels (inward current) or K+ channels (outward current) membrane currents were recorded in voltage‐clamped sensory neurone somata. 1. Depolarization produced a prominent inward Na+ current and a smaller and slower inward Ca2+ current (ICa). The inactivation of ICa was not simply dependent on membrane potential but apparently required prior entry of Ca2+. Two components of outward current, voltage‐activated and Ca2+‐activated, were evident in most cells. 2. The effect of NA, and also of GABA and 5‐HT, was shown to result from a direct effect on ICa because: NA decreased the TTX‐resistant tail current recorded at EK and also the inward current recorded in the presence of 125 mM‐TEA and TTX (in which Na+ and K+ currents were blocked). 3. The decrease in ICa is most likely due to an effect on the number of available Ca2+ channels and/or the single Ca2+ channel conductance rather than to a shift in either the kinetics of channel activation or the Ca2+ equilibrium potential. 4. No effect of the several transmitters on the voltage‐dependent Na+ and K+ currents was observed. 5. Implications of ICa modulation for the phenomenon of presynaptic inhibition are discussed.