A, outward currents recorded at +22 mV in the presence of spermine. The open time decreased dependently on the spermine concentration. B, the steady-state open probability-membrane potential relations. Smooth lines are fits of a Boltzmann function to averaged data (n = 3–5). The voltages of half-activation and slope factors were +35.9 mV and 7.2 mV in the control (▪), +21.4 mV and 5.3 mV with 1 nm spermine (•), +12.4 mV and 4.5 mV with 10 nm spermine (▴), and − 2.1 mV and 5.8 mV with 100 nm spermine (▾).