Fig. 2.

Electrophysiological properties of octopus cells.A, Left, Responses of an octopus cell to steps of current between 2.8 and −2.8 nA in 0.4 nA increments. Responses to depolarizing current pulses are characterized by strong outward rectification. Inward rectification is visible in responses to hyperpolarizing current pulses as a delayed depolarizing sag. A, Right, Action potentials were small (14 mV) and narrow (0.3 msec base width) and could be evoked at the onset and offset of the large depolarizing and hyperpolarizing current pulses, respectively. Subthreshold responses to depolarizing current show a prominent “hump” at their onset (e.g., arrow).B, The voltage–current relationship of the same cell measured at the peak and steady-state of the responses shown inA (circles and squares, respectively). The steady-state input resistance within −5 mV of rest was 2.4 MΩ. C, The membrane time constant of the cell shown in A, measured from a 1.4 mV hyperpolarizing pulse, was described by a single exponential function (dark trace) and was 0.16 msec.