The effect of temperature on the sodium and potassium permeability changes in myelinated nerve fibres of Xenopus laevis

Abstract

The purpose of the present investigation was to determine the effects which changes in temperature have on the constants governing the permeability changes in the myelinated nerve fibre. Voltage clamp experiments were carried out with the node under investigation at various temperatures. The membrane current records so obtained were then analysed as in previous investigations (Frankenhaeuser, 1960(Frankenhaeuser, , 1963 and the rate constants am, Pm' Oh /Ah, oan and fn, and the permeability constants PNa and P'K were calculated. The temperature coefficients (Qlo) were then determined from these data.The significance of the constants is apparent from the following equations PNa = PNa m2h,PNa and P'K are constants with dimensions of permeability; m, h and n are dimensionless variables which can vary between 0 and 1; a and P are rate constants which vary with membrane potential but not with time, and have dimensions of (time)-'.Since a complete voltage clamp analysis is a rather tedious task it was decided to restrict the analysis to a few potential steps only. These potential steps were chosen such that a relatively reliable determination of one rate constant at each step was obtained in a simple manner. METHODSThe experiments were performed on single nodes of Ranvier in large isolated myelinated nerve fibres of the clawed toad (Xenopus laevi8). The membrane potential of node No was changed in rectangular steps by the aid of a feed-back amplifier system as described in previous reports (Dodge & Frankenhaeuser, 1958, 1959. The node No was kept in a con. 28-2

Effects of [Ca2+]i and temperature on minK channels expressed in Xenopus oocytes

“…A modest temperature dependency with a Qio between t .5 and 2.5 has been reported for rapid activating, voltage-gated Na +-and K+-currents in neuronal as well as in muscle tissues [16,17]. Considering the well-defined complex molecular structure of these classical voltage-gated ion channels such minor effects of temperature changes are not surprising, since for channel activation rather small conformational changes of the channel protein are sufficient.…”

Voltage clamp experiments in striated muscle fibres

“…Nastuk & Hodgkin, 1950;Hodgkin & Katz, 1949) Rougier et al (1968) with our own. In myelinated axons Frankenhaeuser & Moore (1963) found temperature coefficients ranging from Qlo = 1-7 to 3-2. The equivalent circuit was that proposed by Falk & Fatt (1964) and is shown in Fig.…”

Synaptic transmission in the neocortex during reversible cooling

“…However, most of these studies were done on preparations from invertebrates or lower vertebrates, 16,18,20,24,26,37,41,55 while there is only limited data from higher vertebrate. 2,5,27,44,51 However, there are indications that temperature dependence of the functioning of mammalian and non-mammalian cells can be quite different 26 (cf.…”