Depolarization-Induced Ca2+ Entry Preferentially Evokes Release of Large Quanta in the Developing Xenopus Neuromuscular Junction

Author:

Sun Xiao-Ping1,Chen Bo-Ming1,Sand Olav2,Kidokoro Yoshi13,Grinnell Alan D.1

Affiliation:

1. Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, California;

2. Department of Molecular Biosciences, University of Oslo, Oslo, Norway; and

3. Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan

Abstract

The amplitude histogram of spontaneously occurring miniature synaptic currents (mSCs) is skewed positively at developing Xenopus neuromuscular synapses formed in culture. To test whether the quantal size of nerve-evoked quanta (eSCs) distributes similarly, we compared the amplitude histogram of single quantum eSCs in low external Ca2+ with that of mSCs and found that nerve stimulation preferentially released large quanta. Depolarization of presynaptic terminals by elevating [K+] in the external solution or by direct injection of current through a patch pipette increased the mSC frequency and preferentially, but not exclusively, evoked the release of large quanta, resulting in a second broad peak in the amplitude histogram. Formation of the second peak under these conditions was blocked by the N-type Ca2+ channel blocker, ω-conotoxin GVIA. In contrast, when the mSC frequency was elevated by thapsigargin- or caffeine-induced mobilization of internal Ca2+, formation of the second peak did not occur. We conclude that the second peak in the amplitude histogram is generated by Ca2+ influx through N-type Ca2+ channels, causing a local elevation of internal Ca2+. The mSC amplitude in the positively skewed portion of the histogram varied over a wide range. A competitive blocker of acetylcholine (ACh) receptors, d-tubocurarine, reduced the amplitude of smaller mSCs in this range relatively more than that of larger mSCs, suggesting that this variation in the mSC amplitude is due to variable amounts of ACh released from synaptic vesicles. We suggest that Ca2+ influx through N-type Ca2+ channels preferentially induces release of vesicles with large ACh content.

Publisher

American Physiological Society

Subject

Physiology,General Neuroscience

Cited by 3 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

同舟云学术

1.学者识别学者识别

2.学术分析学术分析

3.人才评估人才评估

"同舟云学术"是以全球学者为主线,采集、加工和组织学术论文而形成的新型学术文献查询和分析系统,可以对全球学者进行文献检索和人才价值评估。用户可以通过关注某些学科领域的顶尖人物而持续追踪该领域的学科进展和研究前沿。经过近期的数据扩容,当前同舟云学术共收录了国内外主流学术期刊6万余种,收集的期刊论文及会议论文总量共计约1.5亿篇,并以每天添加12000余篇中外论文的速度递增。我们也可以为用户提供个性化、定制化的学者数据。欢迎来电咨询!咨询电话:010-8811{复制后删除}0370

www.globalauthorid.com

TOP

Copyright © 2019-2024 北京同舟云网络信息技术有限公司
京公网安备11010802033243号  京ICP备18003416号-3