Fig. 6. Voltage sensitivity of nematocytes in the absence of chemical sensitization. (A) Voltage responses of a nematocyte from Stauridiosarsia to depolarizing current steps, increased in increments of 0.25 nA, starting from –100 mV. At depolarizations above –10 mV a regenerative action potential is elicited. (B) Typical action potential at a threshold of –8 mV, induced by current injection. (C) Voltage responses of a nematocyte from Dipurena to depolarizing current steps, increased in increments of 0.5 nA, starting from resting voltage. At about –40 mV a regenerative, persistent depolarization is triggered, while an action potential occurs at a threshold close to 0 mV. (D) Membrane currents from a Stauridiosarsia nematocyte recorded in discontinuous voltage-clamp mode in response to voltage steps in increments of 10 mV, starting from –70 mV (data are shown with linear leak currents subtracted). (E) Membrane currents from D as a function of membrane potential: steady-state currents (open symbols) are compared to transient values (filled symbols). Transient inward currents activate at about –10 mV, matching the action potentials threshold.