Effects of lectins on quantal release at the frog neuromuscular junction.
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 micrograms/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.
Gu
X Q
XQ
Department of Physiology and Biophysics, State University of New York, Stony Brook 11794-8661.
van der Kloot
W
W
D000818:Animals; D002118:Calcium / Q000502:physiology; D003208:Concanavalin A / Q000494:pharmacology; D066298:In Vitro Techniques; D037102:Lectins; D008766:Methylmannosides / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects / Q000294:innervation; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011894:Rana pipiens; D012462:Saline Solution, Hypertonic; D012584:Sciatic Nerve / Q000187:drug effects
D037102:Lectins; D008766:Methylmannosides; D012462:Saline Solution, Hypertonic; D003208:Concanavalin A; C008466:methylmannoside; D011188:Potassium; D002118:Calcium