Calcium dependence of evoked transmitter release at very low quantal contents at the frog neuromuscular junction

The Journal of Physiology
R Andreu, E F Barrett

Abstract

1. The relationship between the rate of evoked transmitter release and the extra-cellular concentration of Ca ions, [Ca2+]o, was studied at surface neuromuscular junctions of the frog cutaneous pectoris muscle. The average quantal content of the end-plate potential was reduced to low levels by reducing [Ca2+]o and adding 2 mM-Mn2+, 45 MM-Co2+ or 10 mM-Mg2+. 2. When the motor nerve was stimulated at a low frequency (0.5--2 Hz) in 2 mM-Mn2+ or 4 mM-Co2+, the average quantal content of evoked release was proportional to the fourth power of [Ca2+]o down to the lowest measurable quantal contents, around 2--4 quanta per 1000 stimuli. Combined with previous studies, this result indicates that evoked transmitter release has a steep, nonlinear dependence on [Ca2+]0 over our orders of magnitude of evoked release. 3. Calculations predict that if evoked and spontaneous release have the same fourth power dependence on intracellular [Ca2+], then the curve relating evoked release and [Ca2+]o should become much less steep as the evoked release rate approaches the spontaneous release rate. Our observation that the relationship between evoked release and [Ca2+]o remains fourth power down to very low release rates suggests that most spontaneous q...Continue Reading

Citations

Nov 1, 1994·Bulletin of Mathematical Biology·S AharonI Parnas
Feb 1, 2000·Trends in Neurosciences·H ParnasI Parnas
Aug 17, 2002·Trends in Neurosciences·Jen-Wei Lin, Donald S Faber
Jan 5, 2011·The Journal of Cell Biology·Yonatan M KupchikHanna Parnas
Jun 8, 1999·The Journal of Physiology·I Parnas, H Parnas
Jan 11, 2007·Journal of Neurochemistry·Ellya A BukharaevaLev G Magazanik
Jan 1, 1985·British Journal of Clinical Pharmacology·J G Widdicombe
Dec 18, 2002·Proceedings of the National Academy of Sciences of the United States of America·Hanna ParnasLee A Segel
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Jan 1, 1991·Annals of the New York Academy of Sciences·I ParnasB Hochner
Oct 22, 2017·Toxicon : Official Journal of the International Society on Toxinology·Phillip H BeskePatrick M McNutt

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