Neurotransmitter release and its facilitation in crayfish. II. Duration of facilitation and removal processes of calcium from the terminal
Parnas, I.; Parnas, H.; Dudel, J.
Pflugers Archiv European Journal of Physiology 393(3): 232-236
1982
ISSN/ISBN: 0031-6768 PMID: 6124930 Document Number: 190242
Excitatory postsynaptic currents were recorded extracellularly from synaptic spots on crayfish opener muscles. Facilitation was measured in twin pulses with different intervals. When the extracellular Ca concentration, Ca 0, was raised from 1.7 to 13.5 mM, the duration of facilitation was increased more steeply than can be explained by the higher entry of Ca. The discrepancy can be accounted for by assuming 2 saturable Ca removal processes, one being inhibited at high Ca 0. If Na 0 was reduced to 50 or 25%, facilitation at low Ca 0 (e.g. 3.4 mM) was greatly prolonged, while at high Ca 0 (13.5 mM) no effect was observed. One of the Ca removal processes, R1, depends on Na 0 and is inhibited by Ca 0; probably it is a Ca1 .fwdarw. Na0 exchange. R1 is predominant at low Ca 0 and is largely responsible for the short duration of facilitation there. Other removal processes, R2, are not affected appreciably by Ca 0 and Na 0, and they predominate at high Ca 0. Approximate values for the kinetic constants of R1 and R2 and the inhibition of R1 were estimated.