HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dulhunty, A F Articles by Gage, P W Search for Related Content PubMed PubMed Citation Articles by Dulhunty, A F Articles by Gage, P W

Asymmetrical charge movements (Q) were recorded from the voltage-clamped ends of muscle fibres in extensor digitorum longus (e.d.l.) and soleus muscles from rats. Tetracaine (2 mM) was added to solutions to prevent contraction. In both muscles the relationship between Q and membrane potential (V) was S-shaped and could be described by the Boltzmann-type equation Q = Qm/(1 + exp[-(v - V)/k]) where Qm was the maximum charge, V the membrane potential at which Q = Qm/2, and k a 'slope factor'. On average, Qm was 5-6 times greater in e.d.l. than in soleus fibres and charge movement occurred at more negative potentials in soleus than in e.d.l. fibres, V being -36.7 mV in the former and -19.0 mV in the latter, a difference of about 18 mV. The threshold for contraction, determined using a two-electrode voltage clamp, was more negative in soleus than in e.d.l. fibres. For 500 ms depolarizations, the difference was 12 mV. The relationship between tension and membrane potential during potassium contractures was S-shaped and, when fitted by the Boltzmann-type equation, gave V values of -25 mV for soleus and -14 mV for e.d.l. fibres. In paraplegic rats, the threshold for contraction in soleus fibres shifted about 12 mV to more positive potentials, but there was no change in e.d.l. fibres so that there was no significant difference between the two muscles. In paraplegic rats the relationship between tension and membrane potential during potassium contractures also shifted to more positive potentials in soleus fibres, whereas there was no change in e.d.l. fibres. These changes in the voltage sensitivity of contractile activation in soleus fibres from paraplegic rats were associated with a parallel shift in the voltage sensitivity of charge movement so that the average V shifted from -36.7 mV in normal rats to a value of -14.2 mV in paraplegic rats. There was also a four-fold increase in Qm in soleus fibres from paraplegic rats. The difference between the voltage sensitivity of contractile activation and charge movement in e.d.l. and soleus fibres in normal rats supports the hypothesis that the two are closely related: even stronger support comes from the observation of the parallel shift in the voltage sensitivity of contractile activation and charge movement in soleus fibres in paraplegic rats.

This article has been cited by other articles:

				G. S. Posterino and S. L. Dunn Comparison of the effects of inorganic phosphate on caffeine-induced Ca2+ release in fast- and slow-twitch mammalian skeletal muscle Am J Physiol Cell Physiol, January 1, 2008; 294(1): C97 - C105. [Abstract] [Full Text] [PDF]

				W. A. Macdonald and D. G. Stephenson Effect of ADP on slow-twitch muscle fibres of the rat: implications for muscle fatigue J. Physiol., May 15, 2006; 573(1): 187 - 198. [Abstract] [Full Text] [PDF]

				J. S. Otis, R. R. Roy, V. R. Edgerton, and R. J. Talmadge Adaptations in metabolic capacity of rat soleus after paralysis J Appl Physiol, February 1, 2004; 96(2): 584 - 596. [Abstract] [Full Text] [PDF]

				C. Goodman, M. Patterson, and G. Stephenson MHC-based fiber type and E-C coupling characteristics in mechanically skinned muscle fibers of the rat Am J Physiol Cell Physiol, June 1, 2003; 284(6): C1448 - C1459. [Abstract] [Full Text] [PDF]

				C. Collet, L. Csernoch, and V. Jacquemond Intramembrane Charge Movement and L-Type Calcium Current in Skeletal Muscle Fibers Isolated from Control and mdx Mice Biophys. J., January 1, 2003; 84(1): 251 - 265. [Abstract] [Full Text] [PDF]

				Z. Zheng, Z.-M. Wang, and O. Delbono Insulin-like Growth Factor-1 Increases Skeletal Muscle Dihydropyridine Receptor alpha 1S Transcriptional Activity by Acting on the cAMP-response Element-binding Protein Element of the Promoter Region J. Biol. Chem., December 20, 2002; 277(52): 50535 - 50542. [Abstract] [Full Text] [PDF]

				R. J. Talmadge, R. R. Roy, V. J. Caiozzo, and V. R. Edgerton Mechanical properties of rat soleus after long-term spinal cord transection J Appl Physiol, October 1, 2002; 93(4): 1487 - 1497. [Abstract] [Full Text] [PDF]

				S. Pierno, J.-F. Desaphy, A. Liantonio, M. De Bellis, G. Bianco, A. De Luca, A. Frigeri, G. P. Nicchia, M. Svelto, C. Leoty, et al. Change of chloride ion channel conductance is an early event of slow-to-fast fibre type transition during unloading-induced muscle disuse Brain, July 1, 2002; 125(7): 1510 - 1521. [Abstract] [Full Text] [PDF]

				M. W. Berchtold, H. Brinkmeier, and M. Muntener Calcium Ion in Skeletal Muscle: Its Crucial Role for Muscle Function, Plasticity, and Disease Physiol Rev, July 1, 2000; 80(3): 1215 - 1265. [Abstract] [Full Text] [PDF]