Fig. 4. Steady-state inactivation and recovery from inactivation of the low-voltage-activated calcium current. Sr²⁺ was used as the charge carrier. (A) The steady-state inactivation curve was obtained from data generated using 20 ms test pulses to -30 mV immediately following 2 s conditioning prepulses in 5 mV increments from -110 to -30 mV. The holding potential prior to the conditioning pulse was -80 mV. Steady-state inactivation data were normalised to averaged maximal current (I/I_max) and the means fitted with a Boltzman equation (I/I_max=1/{1+exp[(V_pp-V₅₀)/k]}, where V_pp is the prepulse voltage, V₅₀ is the prepulse voltage causing half-inactivation; k is the slope factor of the inactivation curve in mV per e-fold change). V₅₀=-80±3.5 mV, k=7.7±1.9 mV, N=7. (B) The curve for recovery from inactivation was generated from data obtained using 20 ms inactivating prepulses to -30 mV from a holding potential of -80 mV, followed by a recovery period (R_t) of variable duration from 6.4 to 800 ms at -80 mV, and a 25 ms test pulse to -30 mV. Peak currents obtained in response to test pulses were normalised to prepulse values (I/I_max) and fitted with exponential curves (I/I_max=1-exp(-R_t/), where R_t is the recovery period and is the time constant). =51.7±0.8 ms. Values are means ± S.E.M., N=10.

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