Key Points
- Identify and characterize outward potassium currents in bullfrog sympathetic neurons, focusing on the biophysical properties of the M-current.
- Performed in vitro two-microelectrode voltage-clamp recordings on isolated bullfrog lumbar sympathetic neurones.
- Measured voltage sensitivity, activation and deactivation kinetics, and steady-state current-voltage relationships across membrane potentials.
- Identified four distinct outward K+ currents: delayed rectifier (IK), calcium-dependent (IC), transient (IA), and the novel non-inactivating M-current (IM).
- Characterized IM as having an activation threshold at -60 mV, half-activation at -35 mV, maximal conductance of 84 +/- 14 nS per neuron, and a maximum kinetic time constant of ~150 ms at -35 mV (22 °C).
- Demonstrated that time- and voltage-dependent opening of M-channels induces rectification between -60 and -25 mV, exerting a potential-clamping effect subthreshold to excitation.
Structured PICO
PPopulationBullfrog lumbar sympathetic neurones in vitro
IInterventionVoltage-clamp through twin micro-electrodes
OOutcomeIdentification and characterization of outward (K+) currents, specifically the M-current (I(M))surrogate
Identifies and characterizes the M-current, a novel non-inactivating potassium current in bullfrog sympathetic neurons that exerts a strong potential-clamping effect at subthreshold membrane potentials.