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-51689092
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Neurons IonicCurrents
68 records
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prepulse to -100 mV, there was an additional transient component of inward
current, with a threshold for activation at about -60 mV (low-threshold or
T-type Ca2+ current). The I-V relation for this current (the difference
between the records with and without the prepulse) is plotted as open circles
for the example cell in Fig. 2B. The maximum low-threshold current was evoked
at about -30 mV and was 47+-31 pA (n = 30; excludes 2 cells in which the
current was absent or unmeasurably small, and one in which the leak
subtraction was unsatisfactory)."p.1598
"Steady-state inactivation of the low-threshold Ca2+ current was examined in
four neurons by stepping to a constant test voltage from various prepulse
potentials (each 800 ms duration). Figure 3A shows the inactivation curve
based on data from four cells and example records from one cell. In each
neuron the maximum current was normalized to 1.0 (i.e., inactivation fully
removed), and the data points were then averaged across cells. A Boltzmann
curve was fitted by an algorithm that minimized the sum of squared errors. The
slope factor for the fitted curve was 5.4 mV per e-fold change. The
low-threshold current was almost fully inactivated at -70 mV; inactivation was
half removed at -86 mV and fully removed at about -110 mV."p.1599
"The time course for removal of inactivation of the low-threshold current was
investigated in two neurons. The results from one are shown in Fig. 3B. The
low-threshold current was evoked after hyperpolarizing prepulses of constant
amplitude [to -95 mV in one cell (Fig. 3B) and -110 mV in the other]. In both
cases removal of inactivation occured over hundreds of milliseconds and
appeared almost complete by 800 ms (these cells became progressively leaky
when the durations of hyperpolarizations exceeded 1 s, so longer prepulses
were not examined). These findings indicate that both strong (more negative
than -100 mV) and prolonged (hundreds of ms) hyperpolarization is required for
inactivation of the low-threshold current to be fully removed."p.1599
