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Titolo:
QUANTAL TRANSMITTER RELEASE AT SNAKE TWITCH AND TONIC MUSCLE-FIBERS DURING PROLONGED NERVE-TERMINAL DEPOLARIZATION
Autore:
CONIGLIO LM; HARDWICK JC; PARSONS RL;
Indirizzi:
UNIV VERMONT,COLL MED,DEPT ANAT & NEUROBIOL BURLINGTON VT 05405
Titolo Testata:
Journal of physiology
, volume: 466, anno: 1993,
pagine: 383 - 403
SICI:
0022-3751(1993)466:<383:QTRAST>2.0.ZU;2-X
Fonte:
ISI
Lingua:
ENG
Soggetto:
TRANSVERSUS ABDOMINIS MUSCLE; FROG NEUROMUSCULAR-JUNCTION; VERTEBRATE SLOW MUSCLE; GARTER SNAKE; FIBER TYPES; ACETYLCHOLINE; DESENSITIZATION; INNERVATION; PROPIONATE; POTASSIUM;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
30
Recensione:
Indirizzi per estratti:
Citazione:
L.M. Coniglio et al., "QUANTAL TRANSMITTER RELEASE AT SNAKE TWITCH AND TONIC MUSCLE-FIBERS DURING PROLONGED NERVE-TERMINAL DEPOLARIZATION", Journal of physiology, 466, 1993, pp. 383-403

Abstract

1. Miniature endplate currents (MEPCs) were recorded in vitro from voltage-clamped twitch and tonic muscle fibres in costocutaneous musclesof the garter snake, Thamnophis. Recordings were made from fibres in a control sodium-containing solution and then during exposure to an isotonic potassium solution containing either 1.0 mm calcium and 4.2 mM magnesium or 3-6 mM calcium. The experiments were done at two levels of external calcium in order to demonstrate that the change in MEPC frequency was calcium dependent. During the initial exposure, to the isotonic potassium solutions. the MEPC frequency was increased manyfold atboth twitch and tonic fibres, but it declined progressively with continued exposure. MEPCs were recorded from both fibre types throughout a20 h exposure to the isotonic potassium solution with 1 mM calcium, but no MEPCs were recorded at most twitch endplates after approximately6 h in the isotonic potassium solution containing 3.6 mm calcium. In contrast, MEPCs were still present at tonic fibre endplates after 20 hin the isotonic potassium solution containing 3.6 mM calcium. 2. After 30 min in the isotonic potassium solution with 1 mM calcium, the MEPC amplitude recorded from both fibre types was approximately twice that in the control sodium-containing solution. At tonic endplates, the MEPC amplitude was also twofold greater in the isotonic potassium solution with 3.6 mm calcium than in sodium-containing solution. In contrast, after 30 min in the isotonic potassium solution containing 3.6 mm calcium, the MEPC amplitude at twitch endplates was similar to that in control solution. 3. In both fibre types, MEPC amplitude decreased progressively with continued exposure to the isotonic potassium solutions. The progressive decrease in MEPC amplitude was not due to a gradual decrease in postsynaptic sensitivity to acetylcholine. 4. The effects of high potassium were reversible as MEPCs were recorded at twitch fibre endplates in preparations which were returned to the control sodium-containing solution after a 20 h exposure to the isotonic potassium solution containing 3.6 mM calcium. 5. Ultrastructural examination showed that after a 6 h exposure to the isotonic potassium solutions most nerve terminals innervating twitch fibre endplates were devoid of synaptic vesicles whereas at the same tine many synaptic vesicles were present in the nerve terminals innervating tonic fibre endplates. Surprisingly, numerous synaptic vesicles were present in nerve terminals innervating either fibre type in muscle preparations exposed to the isotonic potassium solutions for 20 h. 6. The results of the present study demonstrate that nerve terminals innervating tonic fibres can sustain transmitter release at high levels longer that nerve terminals innervating twitch fibres.

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Documento generato il 26/11/20 alle ore 11:17:52