Some effects of aliphatic hydrocarbons on the electrical capacity and ionic currents of the squid giant axon membrane.

Abstract

The electrical properties of squid giant axons were examined by means of admittance bridges at frequencies from 0.5-300 kHZ. A simple equivalent circuit was used to estimate membrane capacity. The calculated membrane capacities decreased monotonically over the whole frequency range. At 100 kHz and higher frequencies, the membrane capacity was independent of potential. At frequencies greater than 20 kHz, exposure of the axons to saturated or 0.9 saturated solutions of n-pentane (275-306 .mu.M) reduced the capacity/unit area by 0.1-0.15 .mu.F cm-2. At 1 kHz, the effect of the saturated pentane solutions depended on the membrane potential. In axons having potentials between -60 and zero mV the pentane solutions lowered the capacity; for potentials between -160 and -60 mV they produced little or no change. Saturated solutions of n-hexane, n-heptane and n-octane exhibited qualitatively similar, but quantitatively smaller influences on the membrane capacity; the changes declined as the chain length increased. Under voltage clamp, the peak inward and steady-state outward currents were partially suppressed by the hydrocarbons. Saturated solutions of n-pentane usually reduced the former (reversibly) by 60-80% and the latter by 20-40%. Solutions of n-hexane, n-heptane and n-octane appeared to have successively less effect. Except in deteriorating axons, none of the hydrocarbons produced consistent changes in the passive membrane resistance, the resting potential or in the reversal potential of the transient inward current. Both the changes in the clamp currents and in the membrane capacity were largely, though not usually completely, reversible. In the hydrocarbon solutions, the axons deteriorated more rapidly than normal. Responses of axons of Doryteuthis plei to the hydrocarbons were very similar to those of Loligo forbesi, except that for the former all observed changes were some 5 times faster. The time courses of the peak inward and steady-state outward currents on exposure of the axons to n-pentane resembled the time course of the change in membrane capacity at 100 kHz. The high frequency capacity results imply that, as for lipid bilayers, the membranes become thicker through adsorption of the hydrocarbon.