The temperature changes during and after the discharge of the electric organ in Electrophones electricus

When slices of the main electric organ of Electrophorus are stimulated electrically, the sequence of temperature changes is briefly positive (Q$_{1}$), then negative (Q$_{2}$) and finally positive (Q$_{3}$). The initial temperature rise Q$_{1}$ is only seen when there are several damaged electroplates in the immediate neighbourhood of the thermistor probe, and is regarded as an artifact. The cooling phase Q$_{2}$ is completed within about 70 ms of the electrical discharge, and its average size on open circuit for a single impulse at 22 degrees C is 60 $\mu $cal/g. The final warming phase Q$_{3}$ is about twice as large, measured from the peak of Q$_{2}$, and its average half-time is 37 s. At lower ambient temperatures the size of Q$_{2}$ is greater (Q$_{10}$ about 1$\cdot $6), and Q$_{3}$ reaches completion rather more slowly. The main object of the experiments was to test the prediction made in 1906 by Bernstein & Tschermak that the electric organ should undergo a cooling equal to the warming of the external resistive load minus the heat of ionic mixing. Simultaneous measurements of the size of Q$_{2}$ and of the external electrical work showed that Q$_{2}$ can be considered as consisting of two components, one of which is the load-dependent 'Bernstein' cooling, while the other is the cooling observed on open circuit which is effectively independent of the current drawn. Not more than a fifth of the open-circuit cooling is likely to arise from the presence of a leakage path round the outer edges of the slice of tissue. After considering several alternatives, it is suggested that the bulk of the open-circuit cooling can possibly be attributed to a coupling between the efflux of K$^{+}$ ions through the innervated faces of the electroplates during the plateau of the discharge and a chemical reaction, perhaps involving a synthesis of ATP by reversal of the sodium pump.