Na+ Activates the Slow AHP
The slow AHP appears to be activated, at least in part, by increases in the intracellular concentration of Na+. Bath application of the K+ channel blocker TEA and the Na+ channel poison TTX results in the generation of repetitive Ca2+ spikes but blocks the slow AHP (A1, 2). Recordings in the presence of TEA alone reveal repetitive Na+/Ca2+ spikes and a slow AHP (B1), but block of the Na+ component with TTX results in a block of the slow AHP and uncovers a slow afterdepolarization. This afterdepolarization is activated by Ca2+ entry (not shown). Expanded traces illustrate the action potential response to sinewave current injection during the adaptation period.