TY - JOUR
T1 - Neurotransmitter release and its facilitation in crayfish - IV. The effect of Mg2+ ions on the duration of facilitation
AU - Parnas, H.
AU - Dudel, J.
AU - Parnas, I.
PY - 1982/10
Y1 - 1982/10
N2 - Excitatory synaptic currents (EPSCs) were recorded extracellulary from synaptic spots on crayfish opener muscles. The decay of facilitation after a first pulse was measured by a second pulse given at increasing intervals; the duration of facilitation TF was the interval after which the second EPSC had 1.1 times the amplitude of the first one. Increasing [Mg]0 in the range from 0.5-12.5 mM at low [Ca]0 (1.7-4.5 mM) led to a monotonic prolongation of facilitation. TF showed a S-shaped dependence on [Mg]0, rising very steeply at 2-5 mM [Mg]0. At higher [Ca]0, and also at half normal [Na]0, an increase of [Mg]0 did not affect the decay of facilitation appreciably. As shown before, the decay of facilitation is due to two Cai-removal processes, R1 and R2. Mg0 inhibits only the R1 process, which is also inhibited by high [Ca]0, is dependent on normal [Na]0 and has the characteristics of a Cai√Na0 exchange. As one possible mechanism, competition of Mg0 with Na0 at the extracellular loading site of the exchange is discussed quantitatively.
AB - Excitatory synaptic currents (EPSCs) were recorded extracellulary from synaptic spots on crayfish opener muscles. The decay of facilitation after a first pulse was measured by a second pulse given at increasing intervals; the duration of facilitation TF was the interval after which the second EPSC had 1.1 times the amplitude of the first one. Increasing [Mg]0 in the range from 0.5-12.5 mM at low [Ca]0 (1.7-4.5 mM) led to a monotonic prolongation of facilitation. TF showed a S-shaped dependence on [Mg]0, rising very steeply at 2-5 mM [Mg]0. At higher [Ca]0, and also at half normal [Na]0, an increase of [Mg]0 did not affect the decay of facilitation appreciably. As shown before, the decay of facilitation is due to two Cai-removal processes, R1 and R2. Mg0 inhibits only the R1 process, which is also inhibited by high [Ca]0, is dependent on normal [Na]0 and has the characteristics of a Cai√Na0 exchange. As one possible mechanism, competition of Mg0 with Na0 at the extracellular loading site of the exchange is discussed quantitatively.
KW - Magnesium
KW - Removal of calcium from terminals
KW - Synaptic facilitation
UR - http://www.scopus.com/inward/record.url?scp=0020431965&partnerID=8YFLogxK
U2 - 10.1007/BF00584962
DO - 10.1007/BF00584962
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C2 - 6129610
AN - SCOPUS:0020431965
SN - 0031-6768
VL - 395
SP - 1
EP - 5
JO - Pflugers Archiv European Journal of Physiology
JF - Pflugers Archiv European Journal of Physiology
IS - 1
ER -