Response of delayed (K+) channels to the time-dependent clamping function in squid giant axon. I. Ascending ramps.
Squid giant axons are voltage-clamped with ascending potential ramps whose slopes range from 0.5 mV/msec to 60 mV/msec and delayed (K+) currents are observed. The parametric current-voltage curves exhibit a delay period of minimal current followed by a rapid increase of current toward a final steady state. Both the initial delay and the slope of the subsequent rising phase increase with increasing ramp slope. When the Hodgkin-Huxley equations are used to generate theoretical current-voltage curves, the sharp difference between the delay and rising phases is muted and the ramp slope must be increased to produce an adequate representation of the data. A muted biphasic response is also observed when the current-voltage curves are generated using modified Hodgkin-Huxley parameters and a correction for K+ accumulation in the periaxonal space. These modified equations provide an accurate fit for step-potential clamp current data. Since the ramp experiments include all relevant clamping potentials, the experiments provide a sensitive test for kinetic models of K+ on flow in the delayed (K+) channels of squid giant axon.
D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism* / Q000502:physiology; D003201:Computers; D049832:Decapodiformes / Q000378:metabolism* / Q000502:physiology; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D013997:Time Factors
D011188:Potassium