{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,23]],"date-time":"2026-10-23T00:02:50Z","timestamp":1792713770199,"version":"4.5.0"},"reference-count":52,"publisher":"American Physiological Society","issue":"1","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Journal of Neurophysiology"],"published-print":{"date-parts":[[2001,1,1]]},"abstract":"<jats:p>We investigated the relationship between intraterminal Ca<jats:sup>2+<\/jats:sup>concentration ([Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>) and the frequency of miniature end plate potentials (MEPPs) at the frog neuromuscular junction by use of ratiometric imaging of fura-2-loaded nerve terminals and intracellular recording of MEPPs. Elevation of extracellular [KCl] over the range of 2\u201320 mM resulted in increases in [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>and MEPP frequency. Loading terminals with the fast and slow Ca<jats:sup>2+<\/jats:sup>-buffers bis-( o-aminophenoxy)- N,N,N\u2032,N\u2032-tetraacetic acid-acetoxymethyl (BAPTA-AM) and EGTA-AM resulted in equivalent reductions in the KCl-dependent increases in MEPP frequency. The [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>dependence of MEPP frequency determined by elevation of [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>due to application of 0.1\u201310 \u03bcM ionomycin was similar to that determined when [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>was raised by increasing extracellular KCl. Measurements in 10 mM extracellular KCl revealed that application of the phorbol ester phorbol 12 myristate 13-acetetate (PMA) caused an increase in MEPP frequency while the inactive analogue, 4\u03b1-PMA, did not. PMA application also caused an increase in [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>. The relationship between [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>and MEPP frequency in PMA was the same as was determined by the other methods of raising [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>. Under all conditions tested, our data revealed a low [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>threshold for activation of transmitter release and are consistent with a K<jats:sub>d<\/jats:sub>for [Ca<jats:sup>2+<\/jats:sup>]<jats:sub>i<\/jats:sub>on the order of 1 \u03bcM.<\/jats:p>","DOI":"10.1152\/jn.2001.85.1.287","type":"journal-article","created":{"date-parts":[[2017,12,21]],"date-time":"2017-12-21T10:42:48Z","timestamp":1513852968000},"page":"287-294","source":"Crossref","is-referenced-by-count":56,"title":["Intraterminal Ca<sup>2+<\/sup>and Spontaneous Transmitter Release at the Frog Neuromuscular Junction"],"prefix":"10.1152","volume":"85","author":[{"given":"J. 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