Figure 13. Effect of TTX and low external Na⁺ solutions on pacemaker activity.

A, TTX (1 μM, 10 min) had no effect on pacemaker activity. B, in another cell, application of external solutions containing 90 mM Na⁺ (35 s, top trace), 40 mM Na⁺ (30 s, middle trace) and 5 mM Na⁺ (35 s, bottom trace), progressively increased AHP₁ amplitude, decreased spike frequency and stopped pacemaker activity at -42 mV (middle trace) or -50 mV (bottom trace). The dashed lines indicate -51 mV (A), -52 mV (B, top trace), -50 mV (B, middle trace) and -49 mV (B, bottom trace).