Document Detail

Longitudinal and transversal propagation of excitation along the tubular system of rat fast-twitch muscle fibres studied by high speed confocal microscopy.
MedLine Citation:
PMID:  22155929     Owner:  NLM     Status:  MEDLINE    
Mammalian skeletal muscle fibres possess a tubular (t-) system that consists of regularly spaced transverse elements which are also connected in the longitudinal direction. This tubular network provides a pathway for the propagation of action potentials (APs) both radially and longitudinally within the fibre, but little is known about the actual radial and longitudinal AP conduction velocities along the tubular network in mammalian skeletal muscle fibres. The aim of this study was to track AP propagation within the t-system network of fast-twitch rat muscle fibres with high spatio-temporal resolution when the t-system was isolated from the surface membrane. For this we used high speed confocal imaging of AP-induced Ca(2+) release in contraction-suppressed mechanically skinned fast-twitch fibres where the t-system can be electrically excited in the absence of the surface membrane. Supramaximal field pulses normally elicited a synchronous AP-induced release of Ca(2+) along one side of the fibre axis which propagated uniformly across the fibre. In some cases up to 80 or more adjacent transverse tubules failed to be excited by the field pulse, while adjacent areas responded with normal Ca(2+) release. In these cases a continuous front of Ca(2+) release with an angle to the scanning line was observed due to APs propagating longitudinally. From these observations the radial/transversal and longitudinal AP conduction velocities along the tubular network deeper in the fibre under our conditions (19 ± 1°C) ranged between 8 and 11 μm ms(-1) and 5 to 9 μm ms(-1), respectively, using different methods of estimation. The longitudinal propagation of APs appeared to be markedly faster closer to the edge of the fibre, in agreement with the presence of dense longitudinal connections immediately below the surface of the fibre and more sparse connections at deeper planes within the fibre. During long trains of closely spaced field pulses the AP-elicited Ca(2+) releases became non-synchronous along the fibre axis. This is most likely caused by local tubular K(+) accumulation that produces local depolarization and local slowing of AP propagation. Longitudinally propagating APs may reduce such inhomogeneities by exciting areas of delayed AP onset. Clearly, the longitudinal tubular pathways within the fibre for excitation are used as a safety mechanism in situations where a local depolarization obstructs immediate excitation from the sarcolemma. Results obtained from this study also provide an explanation for the pattern of contractures observed in rippling muscle disease.
Joshua N Edwards; Tanya R Cully; Thomas R Shannon; D George Stephenson; Bradley S Launikonis
Related Documents :
1328299 - Renal tubular responsiveness to atrial natriuretic peptide in sodium-retaining chronic ...
5014729 - The effects of the removal of the somatosensory areas i and ii on left leg-right leg di...
22003859 - Bernstein's long path to membrane theory: radical change and conservation in nineteenth...
22170399 - Laser-patterned stem-cell bridges in a cardiac muscle model for on-chip electrical cond...
19632869 - Microcytosis does not predict serum iron concentrations in anaemic dogs.
23577039 - Airway smooth muscle hypercontractility in asthma.
21320889 - Preferential skeletal muscle myosin loss in response to mechanical silencing in a novel...
2333689 - Chronic otitis externa and otitis media treated by total ear canal ablation and ventral...
20082419 - Leucine attenuates skeletal muscle wasting via inhibition of ubiquitin ligases.
Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2011-12-12
Journal Detail:
Title:  The Journal of physiology     Volume:  590     ISSN:  1469-7793     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  2012 Feb 
Date Detail:
Created Date:  2012-02-02     Completed Date:  2012-06-21     Revised Date:  2013-06-27    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  475-92     Citation Subset:  IM    
School of Biomedical Sciences, University of Queensland, Brisbane, Qld, 4072, Australia.
Export Citation:
APA/MLA Format     Download EndNote     Download BibTex
MeSH Terms
Action Potentials / physiology*
Calcium / physiology*
Microscopy, Confocal
Muscle Contraction / physiology
Muscle Fatigue / physiology
Muscle Fibers, Fast-Twitch / physiology*
Rats, Wistar
Reg. No./Substance:

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

Previous Document:  Incidences and Range of Spontaneous Findings in the Lymphoid and Haemopoietic System of Control Char...
Next Document:  Pro- and anti-angiogenic factors in human skeletal muscle in response to acute exercise and training...