Low threshold calcium T-current IV curve geometry is alterable through the distribution of T-channels in thalamic relay neurons
Low-voltage-activated calcium T-channels enable low-threshold calcium spiking and associated bursting in thalamocortical relay neurons. One measure of this firing pattern is the geometry of the T-current's IV curve, of which the current/voltage (IV) peak is a fundamental index. Using reconstructed neurons, we show here that: (1) in cells with equivalent IV peak currents, physiologically constrained distributions can shift the peak's voltage by 4.8mV  which is just below the resolution at which IV data is usually gathered and corresponds to a change in the single-spike threshold from 5.4 to 29.3pA; (2) in neurons with equivalent IV peak voltages, distribution can shift the peak current by 1.4nA  which is on the order of 30% of maximal T-current in relay cells. Further, we show that these shifts are qualitatively different than those induced by eight other factors. We conclude that channel distribution is a primary factor shaping IV curve geometry.
iv curve thalamic relay neurons bursting t-channel distribution