Response of delayed (K+) channels to the time-dependent clamping functions in squid giant axon. II. Descending ramps, hyperbolae, and exponentials.

Squid giant axons are voltage-clamped with decaying ramp, hyperbolic, and exponential potential functions to determine an input potential function that generates parametric current density vs. membrane potential (I-V) plots best approximating the I-V curves generated from the steady state delayed (K+) current densities at a series of step clamp potentials. The optimum potential function must produce consistent I-V plots over an extended range of decay periods. A five-millisecond step clamp at the largest depolarizing potential in the experiment insures identical initial conditions for all potential functions. Although all parametric I-V curves are sensitive to K+ accumulation in the periaxonal space, the alteration of the I-V curves due to this accumulation is minimized for the hyperbolic and exponential decay functions. The advantages of these functions for the rapid generation of I-V curves are discussed.