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Access resistance was compensated by 70--80\% using the compensation circuit and series resistance prediction.  Tail current data were filtered at 10 kHz and digitized at 20 kHz.  Peak currents and exponential fits were analyzed using the Clampfit software package (Axon instruments, Foster City, CA, USA).  The activation and inactivation time constants for the T-type currents elicited by step pulse protocols were estimated by fitting individual current traces with double exponential functions: $A1(1-exp(-t/\tau1)) $A1(1-exp(-t/\tau\textsubscript{1}))  + A2(1-exp(-t/\tau2))$ A2(1-exp(-t/\tau\textsubscript{2}))$  where $A1$ and $A2$ are the coefficients for the activation and inactivation exponentials, $t$ is time, and $\tau1$ $\tau\textsubscript{1}$  and $\tau2$ $\tau\textsubscript{2}$  are the activation and inactivation time constants, respectively. The smooth curves for channel activation and steady-state inactivation were obtained by fitting the data with a Boltzmann equation: $1/\{1+exp[(V_{50}-V)/S_{act}]\}$, where $V_{50}$ is the potential for half-maximal activation and $S_{act}$ is the slope conductance.  Dose-response curves for Ni\textsuperscript{2+} inhibition of T-type channel currents were derived by fitting the data using a Hill equation: $B = 1/(1 + \textrm{IC}_{50}/[\textrm{Ni}^{2+}]^n)$, where $B$ is the normalized block, $\textrm{IC}_{50}$ is the concentration of $\textrm{Ni}^{2+}$ giving half maximal blockade, and $n$ is the Hill coefficient.