Electrical responses to mechanical stimulation of the membrane of squid giant axons

The mechano-electrical transduction in the squid axon was studied. A certain volume of solution was intracellularly injected, subsequently redrawn, by a microsyringe, and the resultant expansion and shrinkage of the cell was employed as the mechanical stimulus. Upon stimulation, two types of responses appeared: a depolarizing response and a hyperpolarizing response. The former appeared on large stimulation, but the shape and magnitude were variable even with the same stimulation, and the recovery was very slow. The latter appeared constantly on small stimulation. This hyperpolarizing response was associated with an increase in membrane conductance. Application of inward current through the membrane reversed the sign of the response. The reversal potential was 5-15 mV more negative than the resting potential. It was greatly affected by extracellular K+ concentration. Tetraethylammonium, applied intracellularly, reduced the amplitude of the hyperpolarizing response. However, 4-aminopyridine, tetrodotoxin, and procaine did not affect the response at all. The response became larger when the temperature was reduced. It is possible that the mechanically-induced hyperpolarizing response arises from an increase of potassium and leakage conductance.