Temperature dependence of non-electrolyte and sodium permeability in giant axon of squid.

1. The efflux of [(14)C]urea was measured in micro-injected axons at 18 degrees C. A permeability constant for urea of (0.55 +/- 0.18) x 10(-6) cm/sec was calculated from these experiments.2. The influxes of urea, thiourea, ethylene glycol, urethane and toluene were measured in perfused axons at 18 +/- 1 degrees C. The permeability constants obtained from these determinations increased in the order listed, from (0.76 +/- 0.19) x 10(-6) cm/sec for urea to 0.80 x 10(-4) cm/sec for toluene.3. The influxes of tritiated water and sodium ions at 18 degrees C were measured in perfused axons. An average permeability of (0.78 +/- 0.22) x 10(-4) cm/sec for titriated water and an average influx of 23 +/- 6 p-mole/cm(2) sec for sodium were obtained.4. Lowering the temperature of the external sea-water bathing the axon from 18 to 5 degrees C produced a decrease of 12% in the permeability of toluene, 30% for tritiated water and urethane, 55% for ethylene glycol and urea and 60% for thiourea. There was a 50% reduction in the influx of sodium for this same temperature change.5. The results obtained with the effect of temperature on permeabilities suggest that the axonal membrane has a non-homogeneous composition. A model based on the assumption of structured aqueous channels in the membrane is postulated.