Figure 4.

Strategy and solutions for isolating various ionic currents using the action potential clamp. Bursts were first recorded in current clamp. The amplifier was then switched into voltage clamp, and the burst waveform was used as the voltage command. Sodium current was isolated as TTX-sensitive current, with 1 μm TTX applied in a solution with reduced (50 mm) sodium to improve voltage control and 105 mm TEA to block potassium currents. Calcium currents were obtained by subtracting the currents elicited in zero calcium (magnesium replacement) from the currents elicited in full calcium (2 mm), with a background of 105 mm TEA to block calcium-activated potassium currents. Potassium currents were derived from TEA subtractions with calcium (KCa + Kv) or without calcium (Kv). Calcium-dependent potassium current was then obtained by subtracting the voltage-dependent potassium current from the total potassium current. Changes in solution are indicated by bold, underlined components.