The major event leading to the activation of a skeletal muscle have been worked out, but there are further details that are important to know if one is to understand this system fully.
The aims of the present proposal are to study some of the excitation-contraction (e-c) coupling steps not yet well-defined, and some mechanisms by which they are controlled: I. - Now that we have found that mechanical fatigue is associated with a lack of activation of groups of myofibrils, we would like to investigate the mechanisms responsible for this failure. All the myofibrils in fatigued fibers can be activated with caffeine, therefore, the primary cause of failure lies in earlier steps of e-c coupling: either the tubular action potential (TAP) fails to propagate all along the T system or the T system-TC signal is altered in some myofibrils. Therefore, we will investigate: a) the TAP spread through the entire tubular network and the extent of the delay between T-system and Ca release from the TC; b) the amount of Ca released by the TC in local regions to see if the failure is due to a block in TC release of Ca; c) the passive electrical properties of the fatigued cells. We would like to know if the same mechanisms leading to fatigue operate in both amphibian and mammalian muscle. II. - The second series of experiments is to determine how the intracellular pH changes during fatigue and if it is related to the myofibrilar inactivation. We will determine the pHi in the micro-environment surrounding the myofibrils and relate this with tension and inactivation of the myofibrils. III. - After we have defined the release by and return of Ca to the TC, we will determine whether the voltage dependent recovery of contractility (repriming) after a prolonged depolarization with K+ is a function of the return of Ca to the TC or if it is associated with release of Ca.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS017048-10
Application #
3397313
Study Section
Physiology Study Section (PHY)
Project Start
1981-04-01
Project End
1992-08-31
Budget Start
1990-09-01
Budget End
1992-08-31
Support Year
10
Fiscal Year
1990
Total Cost
Indirect Cost
Name
University of Maryland Baltimore
Department
Type
Schools of Medicine
DUNS #
003255213
City
Baltimore
State
MD
Country
United States
Zip Code
21201
Gonzalez-Serratos, H; Hilgemann, D W; Rozycka, M et al. (1996) Na-Ca exchange studies in sarcolemmal skeletal muscle. Ann N Y Acad Sci 779:556-60
Rasgado-Flores, H; Gonzalez-Serratos, H; DeSantiago, J (1994) Extracellular Mg(2+)-dependent Na+, K+, and Cl- efflux in squid giant axons. Am J Physiol 266:C1112-7
Rozycka, M; Gonzalez-Serratos, H; Goldman, W (1993) Non-homogeneous Ca release in isolated frog skeletal muscle fibres. J Muscle Res Cell Motil 14:527-32
Perreault, C L; Gonzalez-Serratos, H; Litwin, S E et al. (1992) A chemical method for intracellular loading of the calcium indicator aequorin in mammalian skeletal muscle. Proc Soc Exp Biol Med 199:178-82
Garcia, M C; Gonzalez-Serratos, H; Morgan, J P et al. (1991) Differential activation of myofibrils during fatigue in phasic skeletal muscle cells. J Muscle Res Cell Motil 12:412-24
Castillo, E; Gonzalez-Serratos, H; Rasgado-Flores, H et al. (1991) Na-Ca exchange studies in frog phasic muscle cells. Ann N Y Acad Sci 639:554-7
Gonzalez-Serratos, H; Rasgado-Flores, H (1990) Extracellular magnesium-dependent sodium efflux in squid giant axons. Am J Physiol 259:C541-8
Lundblad, A; Gonzalez-Serratos, H; Inesi, G et al. (1986) Patterns of sarcomere activation, temperature dependence, and effect of ryanodine in chemically skinned cardiac fibers. J Gen Physiol 87:885-905
Alvarez-Leefmans, F J; Gamino, S M; Giraldez, F et al. (1986) Intracellular free magnesium in frog skeletal muscle fibres measured with ion-selective micro-electrodes. J Physiol 378:461-83
Somlyo, A V; McClellan, G; Gonzalez-Serratos, H et al. (1985) Electron probe X-ray microanalysis of post-tetanic Ca2+ and Mg2+ movements across the sarcoplasmic reticulum in situ. J Biol Chem 260:6801-7