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Calcium conductance and firing properties of spinal motoneurones in the turtle.
Author(s) -
Hounsgaard J,
Mintz I
Publication year - 1988
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.1988.sp017059
Subject(s) - apamin , chemistry , tetrodotoxin , nifedipine , biophysics , depolarization , hyperpolarization (physics) , conductance , calcium , extracellular , membrane potential , spinal cord , neuroscience , biochemistry , biology , physics , stereochemistry , organic chemistry , condensed matter physics , nuclear magnetic resonance spectroscopy
1. The contribution of Ca2+ conductance to the firing properties of motoneurones was investigated in transverse slices of the turtle spinal cord. 2. In the presence of tetrodotoxin (TTX), tetraethylamonium (TEA) in low extracellular concentration (less than 5 mM) promoted Ca2+ spikes. In higher concentrations of TEA, a suprathreshold depolarizing current pulse was followed by an after‐discharge of Ca2+ spikes riding on a Ca2+ plateau potential. 3. The Ca2+‐dependent plateau was also promoted by Cs+, 4‐aminopyridine (4‐AP) and apamin. However, Ca2+ spikes during plateaux were an order of magnitude faster when promoted by Cs+ or 4‐AP rather than TEA, and apamin did not promote Ca2+ spikes at all. 4. Ca2+ plateaux but not Ca2+ spikes were blocked by nifedipine. 5. In normal medium all effects of the transient Ca2+ influx during action potentials were attributable to its influence on the slow after‐hyperpolarization. The nifedipine‐sensitive, sustained Ca2+ influx was expressed exclusively as plateau potentials and only under conditions of reduced K+ current. 6. It is concluded that the transient and the sustained Ca2+ fluxes in spinal motoneurones are curtailed by different K+ conductances. The two Ca2+ responses are suggested as being mediated by two different types of Ca2+ channels.