Fig 8. N-type Ca²⁺ channel.

(A) Voltage dependence of steady state activation (m_∞, solid line) and inactivation parameter (h_∞, dashed line) of the modelled channel (Sim. = Simulation). Squares represent the experimental data for h_∞ (Expt. = Experimental data) from [60]. (B) Time constants of activation (τ_m, (dashed line) and inactivation (τ_h, solid line) from the model. The squares represent experimental τ_h from [63]. (C) Ca²⁺-dependent inactivation parameter, h_ca is plotted against log₁₀([Ca]_i(in M)). (D) Rectangular voltage clamp currents obtained from the model (solid lines) and experiments (symbols, [63]). The squares represent current at test potential (t.p.) of 0 mV, the triangles and circles represent those from 10 mV and 20 mV, respectively. The solid lines are the corresponding simulation results. Protocol: The holding potential (h.p.) was −60 mV kept for 105 ms. The t.p.’s, were maintained for 100 ms. (E) The normalized peak I-V relationship obtained from the model (solid line) and experiments (squares, [63]) by rectangular voltage clamp protocol. The h.p. was kept at −60 mV for 100 ms and the test potentials from −50 to 30 mV, each of 100 ms duration were used. The curve was normalized by using the magnitude of peak current recorded at 0 mV. Other model parameters: p_max = 0.0113 cm/s, initial [Ca]_i = 136 nM, initial [Ca]_o = 0.017 mM, E_Ca ∼ 60 mV, RMP = −53.5 mV, soma capacitance = 28 pF and soma diameter = 24 μm. The S values for model fits and their 5% threshold values (given in brackets) are: h_∞ = 0.047 (0.05), I-V curve = 0.127 (0.052), for voltage clamp currents at: 0 mV = 1.636 nA (0.137 nA), 10 mV = 0.578 nA (0.1048 nA) and 20 mV = 0.446 nA (0.067 nA).