The effects of temperature and ions on the current-voltage relation and electrical characteristics of a molluscan neurone

Abstract

1. Current-voltage relations were generated in the Anisodoris giant neurone (G cell) by either current pulses or slow biphasic current ramps.2. Inward-going rectification occurred during hyperpolarization at warm temperatures (10-15 degrees C), but not at cold temperatures (0-5 degrees C) or in the absence of external K.3. Replacing external K with Rb eliminated inward-going rectification in the warm, but produced it in the cold. The removal of external Na, Cl or Ca had no effect upon inward-going rectification.4. At cold temperatures the I-V relation was linear when generated by current pulses, but was non-linear in accordance with the constant field hypothesis when generated by current ramps.5. A high conductance state developed when the membrane was hyperpolarized beyond a critical potential (approximately - 130 mV in the cold, and - 110 mV in the warm) which was dependent upon external Ca, but not upon K, Na or Cl.6. Hysteresis was observed in the ramp-generated I-V relation whenever the cell was polarized into the high conductance state.7. Rectification and the high conductance state appear to involve different mechanisms within the membrane. However, both are dependent upon absolute membrane potential and not the resting potential.8. The axonal-somatic conductance ratio for the G cell was calculated to be between 2 and 10.9. The membrane time constant (200-100 msec) and specific resistance (0.1-1.5 x 10(6) Omega cm(2)) varied with temperature, membrane potential, and external ions in a manner that correlated with changes in the shape of the I-V relation. In addition, the resistance was dependent upon external Ca.10. The K permeability (P(K)), measured during inhibition of inwardgoing rectification, was independent of temperature and membrane potential. However, P(Na) increased with warming.11. The specific capacitance was calculated to be 0.5-1.0 muF/cm(2). The capacitance increased slightly with warming, but was independent of membrane potential and unaffected by reductions in external K or Na.