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Voltage‐dependent activity around the resting potential is determinant in neuronal physiology and participates in the definition of the firing pattern. Low‐voltage‐activated T‐type Ca² +  channels directly affect the membrane potential and control a number of secondary Ca² + ‐dependent permeabilities. We have studied the ability of the cloned T‐type channels (α1G,H,I) to carry Ca² +  currents in response to mock action potentials. The relationship between the spike duration and the current amplitude is specific for each of the T‐type channels, reflecting their individual kinetic properties. Typically the charge transfer increases with spike broadening, but the total Ca² +  entry saturates at different spike durations according to the channel type: 4 ms for α1G; 7 ms for α1H; and >  10 ms for α1I channels. During bursts, currents are inhibited and/or transiently potentiated according to the α1 channel type, with …