The effect of hydrogen-ion concentration on the recovery process in muscle

Muscular exercise, lactic acid, and the supply and utilisation of oxygen.—Part XIV. The relation in man between the oxygen intake during exercise and the lactic acid content of the muscles

Hartree and A. V. Hill (1) have shown in the isolated frog’s muscle that the maximum rate of the recovery heat-production is proportional to the square of the total initial heat liberated by the stimulus. This relation has been amply confirmed by Hartree, in experiments hitherto unpublished on the isolated muscle of the tortoise. Hartree and Hill concluded that the speed of the recovery oxidation is at any moment proportional to the square of the concentration of the reacting bodies present at that moment, and suggested that a bimolecular reaction of some kind, possibly involving two lactic acid molecules, might be the determining agent in the velocity of the recovery oxidation. Up to the present it has not been shown that any substances other than lactic acid and oxygen are directly concerned in the recovery process in muscle, so the above relationship can be put in terms of these substances. Expressed in a formula, (rate of oxidation) ∝ (rate of lactic acid removal) = k (concentration of lactic acid) 2 , where k is a velocity constant. In a recent paper Meyerhof, Lohmann and Meier (2) have shown that isolated frog’s muscle perfused by, or suspended in, an oxygenated Ringer’s solution containing sodium lactate will cause a diminution in the amount of lactate in the perfusing fluid, with an uptake of oxygen and a synthesis of glycogen. In these experiments it was obvious that the lactate ion was the determining factor in exciting the oxidation by which the energy was supplied to effect the synthesis of the glycogen. Moreover, as Hartree and Hill have shown (3), a rise of hydrogen ion concentration alone does not increase, but rather decreases, the speed of the recovery process in muscle. It seemed obvious, therefore, that the lactate ion itself was to be regarded as the governing factor in the speed of oxidation.

The recovery heat-production in oxygen after a series of muscle twitches

Experiments determining the recovery heat-production in oxygen after a short tetanic stimulus have been described on various occasions, e. g. , by Hartree and hill (1) (2) and by Hartree and Liljestrand (3). In employing the results of these experiments to calculate the "oxidative quotient for lactic acid" as defined by Meyerhof (see, for example (4). p. 567), viz.: (Lactic acid removed in recovery) / (Lactic acid-or carbohydrate equivalent-oxidised) a complication arises in respect of the anaerobic delayed heat (see 1, 5 and 6).

Chronotropic response of isolated atria to acid base alterations

The effect of acid-base alterations on spontaneous rate was analysed using isolated atria exposed to cumulative degrees of acidosis produced either by adding HCl or by increasing PCO2 in the incubation medium. Frequncy vs. pH curves were made to assess chronotropic response to acid-base changes. Heart rate was increased in alkalosis and decreased when the pH of the medium was lowered. Both "respiratory" and "metabolic" alterations affected the contraction rate to the same extent. Decreasing pH from normal values seemed to decrease heart rate more than the enhancement produced by the same change in pH towards the alkalotic side. When frequency was plotted as a function of hydrogen ion activity (aH+) a more linear relationship was obtained, either with pure "metabolic" or with "respiratory" acid-base alterations. Increasing (aH+) from normal values seemed to decrease heart rate to the same extent (respiratory alterations) or even less (metabolic alterations) than the enhancement produced by the same change in (aH+) towards the alkalotic side. Neither the increase in rate produced by alkalosis nor the decrease induced by acidosis were prevented by blocking the neurotransmitters by atropine or propranolol.

The individual effects of CO2, bicarbonate and pH on the electrical and mechanical activity of isolated rabbit auricles

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