Low threshold calcium T-current IV curve geometry is alterable through thedistribution of T-channels in thalamic relay neurons

Low-voltage-activated calcium T-channels enable low-threshold calcium spiki ng 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 n eurons, we show here that: (1) in cells with equivalent IV peak currents, p hysiologically constrained distributions can shift the peak's voltage by 4. 8 mV - which is just below the resolution at which IV data is usually gathe red and corresponds to a change in the single-spike threshold from 5.4 to 2 9.3 pA; (2) in neurons with equivalent IV peak voltages, distribution can s hift the peak current by 1.4 nA - which is on the order of 30% of maximal T -current in relay cells. Further, we show that these shifts are qualitative ly different than those induced by eight other factors. We conclude: that c hannel distribution is a primary factor shaping IV curve geometry. (C) 1999 Elsevier Science B.V. All rights reserved.