ISSN:
1573-8221
Keywords:
presynaptic toxins
;
mouse diaphragm
;
spontaneous liberation of mediator
;
phospholipases
;
calcium
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract Phosphorylases A2 (PLA) from bee and cobra venoms cause triphasic changes in the frequency of miniature endplate potentials (MEPPs) recorded in the mouse diaphragm: an initial decrease of liberation of mediator followed by an increase, followed in turn by complete blocking of liberation. Removal of Ca++ from the perfusing solution (to concentrations below 10−9M) prevented the presynaptic effect of the two PLAs. If the PLA was washed off with calcium-free solution, subsequent treatment with standard solution (2 mM Ca++) caused an increase in the frequency of MEPPs. Agents increasing the Ca++ concentration in the axoplasm (K+ ions, hypertonic sucrose, and the uncoupling agent 4, 5, 6, 7-tetra-2-trifluoromethylbenzimidazole) caused an increase in the MEPP frequency in muscles poisoned with PLA. Blocking the liberation of mediator evidently was not caused by exhaustion of its reserves.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00806665
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