Figure 6
Calcium microdomain stability breaks down at decreased T-SR diameters. (A–C) Effect of reductions in T-SR diameter, d, from value adopted in the T-SR model. Computations at constant imposed Ca2+ influx density, Jinflux, diffusion coefficient, D, and T-SR distance, w. (A) Variations in [Ca2+] with time following onset of imposed Jinflux. Note initial instabilities close to the onset of imposition of Jinflux at the reduced T-SR diameters. (B) Resulting variations in steady state [Ca2+] with radial distance from the centre of the T-SR junction; note significant differences in the regions close to the T-tubular and sarcoplasmic reticular (SR) membranes, and the intervening T-SR region with decreasing T-SR diameter, d (C) Mapping of [Ca2+] across a midline axial slice; values of [Ca2+] are scaled linearly with maximum concentration at centre of T-SR junction [Ca2+] to illustrate microdomain characteristics and radial concentration gradients. Marked pluming of Ca2+ microdomain with decreasing T-SR diameter. (D) Dependence of T-SR junctional [Ca2+] at the centre, the edge, and halfway between these upon T-SR diameter. Relationships emerging from plots of [Ca2+]TSRcentre, [Ca2+]TSR50% and [Ca2+]TSRedge, against TSR diameter, d, at constant diffusion coefficient, D, influx density, Jinflux and T-SR distance w.
