Fig. 1.

Fast Na⁺ and slow Ca²⁺ components contribute to total inward current in human colon myocytes. A–C: representative whole cell inward currents recorded from a human colonic circular smooth muscle cell evoked by stepping for 50 ms to −80 through +35 mV in 5-mV intervals from the −100 mV holding potential. Intracellular solution contained 5 mM Na⁺ and no added Ca²⁺, while the extracellular solution containing 150 mM Na⁺ and 2.5 mM Ca²⁺ was exchanged. A: total inward current. B: isolation of the fast component of inward current from the same cell as A by replacing extracellular Ca²⁺ with Mn²⁺. C: isolation of slow component of inward current from the same cell as A and B by replacing extracellular Na⁺ with NMDG⁺. D: average current-voltage relationships of peak inward currents (●, as shown in A), fast (○, B) and slow (▼, C) components of inward current, normalized to the conductance of each of cell. n = 6 cells.