Membrane conductance changes in single nodes of Ranvier, measured by laser-induced temperature-jump experiments.
Temperature-jump experiments on isolated myelinated nerve fibers were done using a pulsed laser system in the Q switched mode. Voltage-clamp and temperature perturbations were used to measure the relaxing ionic conductances of both the Na+ and K+ systems. It is shown that the T jump can be used to probe the K+ and Na+ conductances during non-steady state conditions and thereby elicit relaxation times for a variety of initial states. Temperature-induced K+ conductance relaxation times were consistent with voltage-clamp measurements. The temperature-perturbation experiments were done as a combination of a temperature step and impulse change due to an adsorption of carbon black particles on the nerve. The experiments support the hypothesis that the relaxation times of the K+ system are independent of the previous history of the axon. It is concluded that the K+ conductance is at least a second-order system whose relaxation spectrum is composed of two exponential terms the magnitudes of which are markedly dependent on the initial conditions.
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D004553:Electric Conductivity; D007834:Lasers; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011901:Ranvier's Nodes / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D014981:Xenopus
D000644:Quaternary Ammonium Compounds; D012964:Sodium; D011188:Potassium