Potential‐dependent variations of the intracellular pressure in the intracellularly perfused squid giant axon.

Abstract

SUMMARY1. Intracellular pressure responses were recorded from squid giant axons after the axoplasm was removed by the intracellular perfusion technique. A glass tube was inserted into the axon and the movement of the air-water interface formed on the end of the tube was observed with a Y-shaped fibrescope.2. The intracellular pressure increased and decreased rapidly when an action potential was induced by electrical stimulation. The amplitude of the response was about 10 mPa (or 1 x 10-3 mmH20), which was very large in comparison with that observed in unperfused axons. It was sensitive to extracellular Ca2+.3. The pressure response appeared in an all-or-none manner and could be suppressed by tetrodotoxin. This excluded physicochemical processes on the stimulating electrode or current-supplying electrode as sources of the response. Various other sources of artifacts were also excluded. An extensive removal of the axoplasm by intracellular perfusion with a protease-containing solution and a KCl solution did not eliminate the pressure response.4. The intracellular pressure was membrane potential dependent, increasing upon depolarization and decreasing upon hyperpolarization of the membrane. Under voltage clamp, the relationship between the membrane potential and the pressure response was parabolic with a maximum at + 109 mV (in reference to the resting level). The response did not depend on the membrane current. A much slower response due to electro-osmotic water flow was also detected.5. The pressure response induced by hyperpolarization of the membrane was suppressed by extracellular application of a lidocaine-containing solution, but not by a tetrodotoxin-containing solution.6. These results suggest that the pressure responses arise either from a change in electrostriction across the axolemma or from a change in charge-dependent tension along the axolemma.

Mechanical, thermal, and optical changes of the nerve membrane associated with excitation.

“…Several different methods were employed and the results were all consistent [43]. Independently, TERAKAWA [69,70] confirmed a part of their results. He further added a new finding that the intracellular pressure of the squid giant axon rises transiently on excitation.…”

“…For example, the phase of shrinkage is often much more accentuated than the corresponding after-hyperpolarization, as noted before (see, [70], Fig. 12).…”

“…TASAKI and IWASA [62] showed that when tetraethylammonium was injected intracellularly to a squid giant axon so that the action potential formed a plateau, the corresponding mechanical change was not a reproduction of the time course of the membrane potential change. Under similar conditions, however, TERAKAWA [70] showed that the intracellular pressure change followed the time course of the membrane potential. It might be concluded that the mechanical change is a potential-dependent phenomenon in the sense that the membrane potential is an important determining factor of the mechanical change.…”

“…In unperfused squid axons, the peak of swelling roughly coincided with that of the internally recorded action potential [61]. The peak of shrinkage was also around the C) Internal pressure change TERAKAWA [70] examined the change in intracellular pressure of the squid giant axon. In his method a glass tubing was connected to an end of the axon and the movement of the water surface at its opening was observed with the "Fotonic sensor."…”

“…TERAKAWA [70] performed voltage clamp experiments and determined the relationship between membrane potential and intracellular pressure change. The relationship is quadratic and shows a maximum at about 60 mV of the membrane potential.…”