title: Comparison between the predictions of diffusion-reaction models and localized Ca2+ transients in amphibian skeletal muscle fibers.
abstract: We developed a three-dimensional cylindrical diffusion-reaction model of a single amphibian myofibril in which Ca(2+) release occurred only at the Z-line. The model incorporated diffusion of Ca(2+), Mg(2+), and all relevant buffer species, as well as the kinetic binding reactions between the buffers and appropriate ions. Model data was blurred according to a Gaussian approximation of the point spread function of the microscope and directly compared with experimental data obtained using the confocal spot methodology. The flux parameters were adjusted until the simulated Z-line transient matched the experimental one. This model could not simultaneously predict key parameters of the experimental M- and Z-line transients, even when model parameters were adjusted to unreasonably extreme values. Even though the model was accurate in predicting the Z-line transient under conditions of high [EGTA], it predicted a significantly narrower Ca(2+) domain than observed experimentally. We modified the model to incorporate a broader band of release centered at the Z-line. This extended release model was superior both in simultaneously predicting critical features of the Z- and M-line transients as well as the domain profile under conditions of high [EGTA]. We conclude that a model of release occurring exclusively at the Z-line cannot explain our experimental data and suggest that Ca(2+) may be released from a broader region of the sarcoplasmic reticulum than just the T-tubule-sarcoplasmic reticulum junction.
authors.affiliation: Department of Physiology, UCLA School of Medicine, Los Angeles, California, USA.
authors.forename: David
authors.initials: D
authors.lastname: Novo
authors.forename: Marino
authors.initials: M
authors.lastname: DiFranco
authors.forename: Julio L
authors.initials: JL
authors.lastname: Vergara
mesh_terms: D000663:Amphibians; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D003198:Computer Simulation; D004058:Diffusion; D008274:Magnesium / Q000378:metabolism*; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology*; D011892:Rana catesbeiana; D012519:Sarcoplasmic Reticulum / Q000502:physiology; D012680:Sensitivity and Specificity; D014018:Tissue Distribution
chemical_list: D008274:Magnesium; D002118:Calcium