Holding potential affects the apparent voltage-sensitivity of sodium channel activation in crayfish giant axons.
Sodium channel activations, measured as the fraction of channels open to peak conductance for different test potentials (F[V]), shows two statistically different slopes from holding potential more positive than -90 mV. A high valence of 4-6e is indicated a test potentials within 35 mV of the apparent threshold potential (circa -65 mV at -85 mV holding potential). However, for test potentials positive to -30 mV, the F(V) curve shows a 2e valence. The F(V) curve for crayfish axon sodium channels at these "depolarized" holding potentials thus closely resembles classic data obtained from other preparations at holding potentials between -80 and -60 mV. In contrast, at holding potentials more negative than -100 mV, the high slope essentially disappears and the F(V) curve follows a single Boltzmann distribution with a valence of approximately 2e at all potentials. Neither the slope of this simple distribution nor its midpoint (-20 mV) was significantly affected by removal of fast inactivation with pronase. The change in F(V) slope, when holding potential is increased from -85 to -120 mV, does not appear to be caused by the contribution of a second channel type. The simple voltage dependence of sodium current found at Vh -120 mV be used by to discriminate between models of sodium channel activation, and rules out models with three particles of equal valence.
Ruben
P C
PC
Békésy Laboratory of Neurobiology, Pacific Biomedical Research Center, University of Hawaii, Honolulu 96822.
Starkus
J G
JG
Rayner
M D
MD
D000818:Animals; D003400:Astacoidea; D001369:Axons / Q000378:metabolism*; D055592:Biophysical Phenomena; D001703:Biophysics; D003198:Computer Simulation; D004553:Electric Conductivity; D007700:Kinetics; D008564:Membrane Potentials; D015222:Sodium Channels / Q000378:metabolism*
D015222:Sodium Channels