There were no differences among Ih(+) TH(+), Ih(+) TH(−), and Ih(−) neurons in action potential time to peak (A), duration at half-height (B), or width at base (C) (n = 35, 33 and 26, respectively). In neurons exhibiting a prominent Ca2+-gated fast K+ current, there was no difference among these types of cells in time to the fast K+ minimum (D) or time to the IK(AHP) (E) (n = 23, 22 and 21 for Ih(+) TH(+), Ih(+) TH(−), and Ih(−) neurons, respectively). F, the time to the peak (minimum) of the afterhyperpolarization was significantly longer in Ih(−) neurons than in either TH(+) or TH(−) Ih(+) neurons (Ih(+) TH(+) versus Ih(−) and Ih(+) TH(−) versus Ih(−), P < 0.05).