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Titolo:
TRANSMITTER RELEASE DIFFERS AT SNAKE TWITCH AND TONIC END-PLATES DURING POTASSIUM-INDUCED NERVE-TERMINAL DEPOLARIZATION
Autore:
CONNOR EA; DUNAEVSKY A; GRIFFITHS DJG; HARDWICK JC; PARSONS RL;
Indirizzi:
UNIV VERMONT,DEPT ANAT & NEUROBIOL BURLINGTON VT 05405 UNIV VERMONT,DEPT ANAT & NEUROBIOL BURLINGTON VT 05405 UNIV MASSACHUSETTS,DEPT BIOL,NEUROSCI & BEHAV GRAD PROGRAM AMHERST MA01003
Titolo Testata:
Journal of neurophysiology
fascicolo: 2, volume: 77, anno: 1997,
pagine: 749 - 760
SICI:
0022-3077(1997)77:2<749:TRDAST>2.0.ZU;2-6
Fonte:
ISI
Lingua:
ENG
Soggetto:
TRANSVERSUS ABDOMINIS MUSCLE; GARTER SNAKE; NEUROMUSCULAR-JUNCTION; ACTIVE ZONES; SLOW MUSCLE; FIBER TYPES; ACETYLCHOLINE; IMPULSES; BARIUM; INNERVATION;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Science Citation Index Expanded
Citazioni:
28
Recensione:
Indirizzi per estratti:
Citazione:
E.A. Connor et al., "TRANSMITTER RELEASE DIFFERS AT SNAKE TWITCH AND TONIC END-PLATES DURING POTASSIUM-INDUCED NERVE-TERMINAL DEPOLARIZATION", Journal of neurophysiology, 77(2), 1997, pp. 749-760

Abstract

Twitch and tonic muscle fibers of snake skeletal muscle differ in their synpatic as well as mechanical properties. These experiments were aimed at determining the basis of the difference in vesicular release properties of nerve terminals at twitch and tonic endplates. Miniature endplate currents (MEPCs) were recorded from voltage-clamped garter snake muscle fibers depolarized by high K+ in either a control Ca2+ or high-Ca2+ solution. MEPC frequency increased at twitch and tonic endplates and remained elevated for 8 h during depolarization in control Ca2. At twitch endplates depolarized in the presence of high Ca2+, an increase in MEPC frequency was followed by a progressive decline. In contrast, MEPC frequency remained elevated in high Ca2+ at tonic endplates. The observed decrease in MEPC freqency at depolarized twitch endplates in high CA(2+) was not a function of the level of depolarization or initial MEPC frequency, nor was it due to a reduction in MEPC amplitude and loss of MEPCs in baseline noise. An optical assay of presynaptic function in :which the activity-dependent dye FM1-43 was used confired that quantal reslease differs at twitch and tonic endplates. Most twitch nerve terminals were labeled by FM1-43 during prolonged depolarization with control Ca2+ or after brief depolarization with high Ca2+. In contrast, the number of twitch nerve terminals and the degree to which they were stained was greatly reduced after prolonged exposure to high K+ and high Ca2+, whereas depolarized tonic endplates were wellstained by FM1-43 during brief and prolonged exposure to high Ca2+. FM1-43 staining also revealed variable levels of quantal release between individual boutons at twitch endplates after prolonged depolarization in high-Ca2+ solution. The observed reduction in presynaptic function at twitch nerve terminals after prolonged depolarization in high-Ca2 solution was reversible and therefore not due to irreversible damageto terminal boutons. MEPC frequency increased at both twitch and tonic endplates when either Sr2+ or Ba2+ was substituted for high Ca2+ during K+-induced depolarization. Over time, in Sr2+ or Ba2+ solutions, MEPC frequency remained elevated at tonic endplates but declined at twitch endplates with a time course similar to that observed in high CA(2). MEPC amplitudes at both endplates remained constant. We conclude that the regulation of quantal release differs in nerve terminals innervating twitch and tonic endplates and postulate that differential intraterminal accumulation of Ca2+ may underlie the observed difference inpresynaptic function.

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Documento generato il 29/11/20 alle ore 00:45:25