EFFECTS OF LECTINS ON QUANTAL RELEASE AT THE FROG NEUROMUSCULAR-JUNCTION

被引:3
作者
GU, XQ [1 ]
VANDERKLOOT, W [1 ]
机构
[1] SUNY HLTH SCI CTR,DEPT PHYSIOL & BIOPHYS,STONY BROOK,NY 11794
关键词
D O I
10.1016/0306-4522(92)90173-Y
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
This work was initiated because pretreatment with concanavalin A was reported to abolish the increase in spontaneous quantal release produced by hypertonic solutions [Gorio A. and Mauro A. (1979) J. gen. Physiol. 73, 245-263]. This suggested that lectins might be valuable tools for investigating the role of glycoproteins in the response to tonicity. We compared muscles soaked for 2 h in hypertonic solution containing concanavalin A with paired muscles soaked in hypertonic solution without lectin. The lectin treatment decreased miniature end-plate potential frequencies in Ringer and in hypertonic solutions compared with the controls. Even after lectin treatment hypertonic solutions and elevated K+ solutions increased miniature end-plate potential frequencies, and the proportional increases were the same as in controls. The lectin treatment lowered baseline frequency, but the preparation still responded to hypertonic solutions. Concanavalin A effects appeared after treatment for more than 1 h and required concentrations of 10-mu-g/ml or higher. Higher concentrations did not produce more effect. Similar results were obtained with four other lectins with different sugar specificities. Treatment in hypertonic solution without lectin produces a similar, but smaller, decrease in baseline frequency. Concanavalin A pretreatment had no detectable effects on evoked release or facilitation. We conclude that the effects of lectins on quantal release are not mediated by binding to a single sugar group. The lectins do not produce a unique effect; they exaggerate the changes produced by hypertonic pretreatment. All of the effects could be accounted for by a reduction in baseline [Ca2+] in the nerve terminal. Such reductions are produced by lectins in many cell types.
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页码:649 / 656
页数:8
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