The action of high hydrostatic pressure on the membrane currents of Helix neurones.

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Abstract
The actions of high hydrostatic pressure (10.4, 20.8 MPa [pascal]) on the membrane currents of Helix neurons were examined under voltage clamp. High hydrostatic pressure (20.8 MPa) reduced the maximum inward current to 0.78 and the delayed outward current, measured at the inward current reversal potential, to 0.75 of their value at atmospheric pressure. High hydrostatic pressure shifted the curve relating the inward current conductance to membrane potential to more positive values but the maximum conductance was unaltered. The rates of activation of the inward and delayed outward currents were slowed by pressure. The steady-state level and time course of inactivation of the inward current was unaffected by high pressure over the investigated range. The effects of high hydrostatic pressure on the fast outward current identified in gastropod neurons by Connor and Stevens (1971) also were examined. 20.8 MPa reduced the current measured at -30 mV to 0.71 of its control value. The activation rate of the fast outward current was slowed by high pressure, but the time constant of inactivation was unchanged. The majority of the effects of high hydrostatic pressure were completely reversible upon decompression. These results are discussed with reference to the effects of high hydrostatic pressure on the action potential and discharge frequency of gastropod neurons. Possible sites and mechanisms of pressure action on the excitable cell are discussed.