The effect of temperature on veratridine action in squid giant axons

Resting membrane potential and intracellular sodium and potassium concentrations were determined at 5 and 21 degrees C in normal and veratridine-treated axons of the squid Doryteuthis plei. 300 microM veratridine produced an increase in the intracellular sodium concentration, which changed from 52 to 284 mM in 10 min of exposure at 21 degrees C, and from 76 to 260 mM at 5 degrees C. Under the same treatment the intracellular potassium concentration changed from 357 to 221 mM (21 degrees C) and from 334 to 194 mM (5 degrees C). All the changes could be prevented by adding 1 microM tetrodotoxin. Veratridine (30, 100 and 300 microM) increased the resting sodium permeability of the giant axon, and the effect was greater at 21 degrees C. The affinity of the membrane for veratridine increases when the nerves are cooled, the three concentrations tested produce maximum activation of the sodium channels at 5 degrees C. But only the higher two concentrations are saturating at 21 degrees C.