The heat production associated with the passage of a single impulse in pike olfactory nerve fibres.

Abstract

SUMMARY1. A study has been made of the temperature changes associated with the passage of a single impulse in the non-myelinated fibres of the pike olfactory nerve.2. The initial heat occurs in two phases: a burst of positive heat, followed by an evolution of negative heat. The positive and negative heats, and the net initial heat, are temperature-dependent.3. At 00 C the measured positive initial heat is 442 /scal/g. impulse;and the corresponding negative initial heat is 48 9 ,ucal/g . impulse. There is thus a net initial heat that is negative, of about 4-7 lical/g . impulse.4. The positive heat has a positive temperature coefficient, being increased by a factor of 1-86 when the temperature is raised from 00 C to 100 C.5. The negative initial heat also increases when the temperature is raised, but less than the positive initial heat. As a result, the net initial heat tends to become positive at higher temperatures.6. Because of temporal dispersion of the action potential over the face of the thermopile, the observed temperature changes are smaller than those that occur at a single point in the nerve close to the stimulating cathode. The value of the positive heat at 00 C corrected for temporal dispersion is estimated to be about 62 /ucal/g . impulse: the corresponding value for the negative heat is about 67 /tcal/g. impulse.7. All records were analysed in terms of only two phases of initial heat (one positive, one negative). No analysis required four phases; but it is J. V. HOWARTH AND OTHERS unclear whether this finding reflects a true absence of four phases, or merely the inability of the recording equipment to resolve them.8. The positive heat seems to be derived from two sources. First, there is a dissipation of the free energy stored in the membrane capacity. Secondly, there is an evolution of heat corresponding with a decrease in entropy of the membrane dielectric with depolarization.

Muscle heat: a window into the thermodynamics of a molecular machine

“…5). With the use of a galvanometer arrangement similar to that described by Howarth (85), sensitivity was such that the voltage output of a single fiber from the frog anterior tibialis muscle at 15°C was ϳ0.5 V in response to a single stimulus.…”

“…The vacuum-deposition thermopiles of Mulieri et al (108) were developed primarily for use with thin rabbit right-ventricular papillary muscles, although the authors pointed out that they were also suitable for thermal measurements of bundles of skeletal muscle fibers. However, the ultimate refinement, in this direction, measurement of the heat produced by a single anterior tibialis muscle fiber from the frog, was nevertheless made by Curtin et al (30,31) using thermopiles of the Hill-Downing type modified along the lines described by Howarth et al (85). Very low heat capacity was achieved by using 20 brazed constantan-chromel thermocouples, flatted to 8-m thickness, insulated between two 6-mthick layers of Kapton film (Fig.…”

Increase in efflux of inorganic phosphate during electrical activity in small non‐myelinated nerve fibres.

“…Very small nonmyelinated nerve fibres, such as those of the olfactory nerve of the pike (see Howarth, Keynes, Ritchie & von Muralt, 1975) or garfish (Easton, 1971), with their much greater area of axonal membrane per unit weight, might be expected to give more pronounced effects on stimulation so that short periods of stimulation could be used with a consequent better temporal resolution of the activity-induced increase in phosphate efflux. For comparison rabbit vagus nerves were used in some experiments.…”

X-ray Scattering Study of Pike Olfactory Nerve: Elastic, Thermodynamic and Physiological Properties of the Axonal Membrane

“…In PON Howarth et al 19 showed that the time-course of the phenomenon closely follows action potential and measured the positive initial heat (68(G11) mcal/g of wet nerve according to the data of Table 1 …”