Subthreshold and near-threshold membrane currents in lobster stretch receptor neurones.

1. The ion currents in the slowly and rapidly adapting stretch receptor neurone of lobster were investigated with respect to their nature and stationary kinetics in sub- and near-threshold voltage regions using electrophysiological and pharmacological techniques. 2. In both neurones the following currents were identified: (a) a tetrodotoxin-sensitive Na current, (b) a tetraethylammonium and 4-aminopyridine-sensitive K current, (c) a Co (or Mn)-sensitive Ca-dependent K current, (d) an ouabain-sensitive pump current and (e) a remaining leak current carried mainly by Na, K and Cl. 3. In suprathreshold voltage regions the balance between the individual membrane currents leads to the formation of a stationary negative conductance (negative slope in the voltage dependence of the ionic current) in the slowly, but not in the rapidly adapting cell. 4. These observations are compatible with the fact that during prolonged suprathreshold stimulation a stationary low frequency impulse during is possible in the slowly adapting cell, whereas in the rapidly adapting cell it is not.