Laser temperature-jump technique for relaxation studies of the ionic conductances in myelinated nerve fibers.
A temperature-jump technique for single nodes of Ranvier has been developed using a pulsed laser system. The temperature perturbation was accomplished by firing the laser beam obtained from a neodymium rod through the solution surrounding a single node. The temperature step was achieved within 1 msec using the laser in the normal mode of operation. During the voltage-clamped steady-state current a temperature jump from 4 degrees C increased the current to a new steady-state value within the time course of the T-jump. This finding suggests that the maximum potassium permeability P(K) has a rapid relaxation time and that the steady-state value of n (the value of potassium permeability divided by its maximum value) is relatively independent of temperature. T-jumps applied during the voltage-clamped sodium currents showed that the sodium permeability changed with a relaxation time that was also shorter than the duration of the normal mode laser output. T-jumps observed during a hyperpolarization or at the resting potential showed no detectable conductance change. When a T-jump immediately preceded a voltage clamp pulse the technique was then used to investigate the effect of changes in the steady-state temperature on the ionic conductances. It was found that the magnitude of the change in membrane current due to a T-clamp was directly related to the level of cathodal polarization.
D000818:Animals; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D004594:Electrophysiology / Q000295:instrumentation; D007700:Kinetics; D007834:Lasers; D008433:Mathematics; D008564:Membrane Potentials; D009413:Nerve Fibers, Myelinated / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013696:Temperature; D014981:Xenopus
D012964:Sodium; D011188:Potassium