FIGURE 1.

Effect of depolarized HP on release flux permeability components and their ratio. (A) Corrected release records taken while the fiber was held at 0 mV and a prepulse to −100 mV for 2 s before the test pulse was applied. (B) Records taken after full repriming at −90 mV. (C) Effect of changing HP from −90 to −70 mV. Fiber 4088, from R. catesbeiana; [fluo-3] ranged from 121 to 290 μM. Time elapsed was 28 min. Initial Ca content of the SR was 800 μM in all cases. Parameters of removal, [EGTA] = 4.5 mM; k_offEGTA = 2.4 μM⁻¹ s⁻¹; and k_onEGTA = 3.2 s⁻¹. (D) Voltage dependence of peak and steady permeability. (E) The p/s ratio. In D and E, HP = −90 mV (black symbols). HP = −70 mV (gray symbols). Brief repriming protocol (unfilled symbols). In D, peak (circles); and steady values of permeability (triangles). Best-fit of a two-states Boltzmann function to the data points (continuous lines). Parameters of the Boltzmann fit, P_SRmax = 13.94 × 10⁻³ ms⁻¹, V^* = −40.18 mV, and k = 4.74 mV for the peak permeability; P_SRmax = 6.27 × 10⁻³ ms⁻¹, V^* = −33.07 mV, and k = 6.28 mV for the steady SR permeability at V_h = −90 mV; P_SRmax = 5.09 × 10⁻³ ms⁻¹, V^* = −26 mV, and k = 7.93 mV for the peak permeability; P_SRmax = 1.16 × 10⁻³ ms⁻¹, V^* = −24.99 mV, and k = 9.7 mV for the steady SR permeability at V_h = −70 mV; P_SRmax = 4.37 × 10⁻³ ms⁻¹, V^* = −14.06 mV, and k = 7.38 mV; and P_SRmax = 5.89 × 10⁻⁴ ms⁻¹, V^* = −22.21 mV, and k = 6.13 mV for the brief repriming protocol.