Activity-dependent reduction in voltage-dependent calcium current in a crayfish motoneuron.
The effect of increased impulse activity upon voltage-dependent Ca2+ currents was studied in the cell body of a crayfish phasic motoneuron using two-electrode voltage-clamp technique. Increased electrical activity in this relatively inactive motoneuron produces a short-term and long-term reduction in the voltage-dependent Ca2+ current. Both forms of activity-dependent reduction in Ca2+ current are Ca2+ dependent. The short-term reduction in Ca2+ current appears to involve the Ca(2+)-dependent inactivation of Ca2+ channels, previously described in a variety of neurons. The long-term reduction in Ca2+ current is produced by prolonged Ca2+ influx and persists for days: in vivo stimulation of the phasic motor axon at 5 Hz for 1 hr results in a 30% reduction in Ca2+ current density, which persists for at least 3 d. Both the short-term and long-term reductions in Ca2+ current appear to result from changes in a single type of high-voltage-activated (HVA) Ca2+ channel. Inhibition of protein synthesis attenuates the long-term reduction in Ca2+ current and has no effect upon the short-term Ca2+ current reduction. During the long-term reduction in Ca2+ current, it appears that Ca2+ channels located distant to the site of Ca2+ influx are affected. The relationship of these results to a previously described Ca(2+)-dependent reduction in transmitter release is discussed.
Hong
S J
SJ
Department of Biological Sciences, University at Albany, SUNY 12222, USA.
Lnenicka
G A
GA
D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000187:drug effects / Q000502:physiology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000502:physiology; D013997:Time Factors
D015220:Calcium Channels; D002104:Cadmium; D003513:Cycloheximide; D002118:Calcium