Skip to main content
. 2004 Nov 4;562(Pt 2):347–365. doi: 10.1113/jphysiol.2004.073882

Figure 8. Calcium input flux and SR permeability calculated from fura-FF fluorescence ratio recordings.

Figure 8

A, fura-FF fluorescence ratio recordings (F380/F360) obtained at four different voltages (−30, −10, +10 and +20 mV). As in the case of the fura-2 recordings (Fig. 1D) a decrease in the ratio indicates an increase in Ca2+ concentration. B, Ca2+ input flux obtained by removal model fitting as described in the text. Best-fit parameter values: koff,Dye= 170 s−1, kon,S= 7.3 μm−1 s−1, koff,S= 6.7 s−1 and kuptake= 3862 s−1. Fixed parameters here and in all other fura-FF analyses had the following values: Rmin= resting R (see Methods), Rmax= 1.5, [Dye]total= 0.2 mm, [S]total= 15 mm and KDye=koff,Dye/kon,Dye= 6.5 μm. As in fura-2 experiments, flux amplitudes were scaled by 0.4 to account for lower concentrations of [Dye]total and [S]total in the cell (see Methods and Results). C, peak (○) and plateau component (□) of Ca2+ input flux derived from six fura-FF experiments plotted as functions of voltage. Data were fitted as described in Fig. 4C. ⋄, measurements at +20 mV, 1 min before and after the series of test pulses indicating the degree of run-down in peak flux. The fit parameters V1/2, k, a and b had mean values of −8.03 ± 2.12 mV, 8.54 ± 0.53 mV, 212 ± 65.2 μm ms−1 and 0.12 ± 0.57 μm ms−1 V−1, respectively, for the peak, and −10.87 ± 2.18 mV, 7.48 ± 0.45 mV, 29.7 ± 4.04 μm ms−1 and 0.16 ± 0.04 μm ms−1 V−1, respectively, for the plateau. Estimated SR contents at +10, +20, +30, +40 and +50 mV were 7.77 ± 1.32, 5.98 ± 0.49, 6.46 ± 1.02, 5.6 ± 0.58 and 5.15 ± 0.51 mm, respectively. D, voltage dependence of the corresponding permeabilities derived from the data in C. Values of the fit parameters (see C) were −4.37 ± 4.07 mV, 9.92 ± 0.51 mV, 3.28 ± 0.77% ms−1 and 19.25 ± 12.09% ms−1 V−1, respectively, for the peak, and −7.99 ± 4.64 mV, 7.61 ± 0.68 mV, 0.678 ± 0.137% ms−1 and −0.64 ± 0.99% ms−1 V−1, respectively, for the plateau. The Ca2+ input flux calculations were based on a removal model with the following set of parameters: [fura-FF]= 0.2 mm, [EGTA]= 15 mm, Rmin= resting R, Rmax= 1.50, KDye= 6.5 μm, koff,Dye= 192 ± 30 s−1, kon,S= 11.0 ± 1.8 μm−1 s−1, koff,S= 4.94 ± 1.26 s−1, kuptake= 4.00 × 103± 0.77 × 103 s−1. The parameters koff,Dye, kon,S, koff,S and kuptake were optimized by the removal model fit procedure as described in Results.