The effect of osmotic gradients on the outward potassium current in dialyzed neurons of Helix pomatia.

1. The effect of outward and inward water flows through the membrane on outward potassium currents of dialyzed Helix pomatia neurons was studied. 2. An outward water flow increased the peak and sustained outward potassium currents and accelerated the kinetics of their activation. An inward water flow had quite opposite effects--it decreased the peak and sustained potassium currents and delayed the kinetics of their activation. 3. The analysis of the effect of water flow on the conductance of potassium channels showed that an outward water flow increased both the potassium conductance at a given potential (gk) and the maximum potassium conductance (gkmax). An inward water flow again had the opposite effect--it decreased the potassium conductance at given potential and the maximum potassium conductance. 4. Neither an outward nor an inward water flow significantly affected the fraction of open potassium channels at a given potential [n infinity(V)]. 5. These data suggest that in dialyzed neurons the changes of outward potassium current during water flow through the membrane are due mainly to the changes in single-channel conductance and the time constant of current activation.