Microcalorimetric determination of energy expenditure due to active sodium‐potassium transport in the soleus muscle and brown adipose tissue of the rat.

Abstract

SUMMARY1. The resting heat production rate (E) of soleus muscles from young rats and brown adipose tissue from adult rats was measured by means of a perfusable heat flux microcalorimeter in the absence and presence of ouabain. In the soleus muscle, the acute response of E to ouabain was compared with the ouabain-suppressible components of 22Na-efflux and 42K-influx.2. In standard Krebs-Ringer bicarbonate buffer, ouabain (10-3M) induced an immediate but transient decrease in E of around 5 %. Both in muscle and adipose tissue this was followed by a progressive rise in heat production rate.3. When the medium was enriched with Mg (10 mM), ouabain produced a sustained decrease in E of the same magnitude as in the standard medium and the secondary rise was less marked or abolished. Under these conditions, in the soleus muscle, ouabain inhibited E? by 5 % (i.e. by 1-76 + 0-22 mcal.g wet wt.-'.min-'), 22Na-efflux by 58 % (0.187 + 0.013,mole. g wet wt. -. min-') and 42K-influx by 34 % (0.132 ± 0028 molel. g wet w.l.min-1).4. When the muscles were loaded with Na by pre-incubation in K-free Mg-enriched medium, the addition of K (3 mM) induced an immediate ouabain-suppressible increase in E of 2 98 + 0 33 mcal. g wet wt.-. minand a concomitant stimulation of 22Na-efflux of 0-388 + 0 136 molel. g wet wt.-. min-.5. Maximum Na/ATP ratios for the active Na-K transport process were computed, with no assumption as to the in vivo free energy of ATP hydrolysis. These were 2 1, 1 9 and 2-3 under the conditions described in paragraphs (2), (3) and (4) respectively. 44A. CHINET, T. CLAUSEN AND L. GIRARDIER 6. The calculated reversible thermodynamic work associated with active Na-K transport corresponded to 34 % of the measured ouabaininduced decrease in P. On the premise that the maximum efficiency of the cellular energy conservation processes is 65 %, this estimate indicates that the minimum energetic efficiency of ATP utilization by the active Na-K transport process in mammalian muscle is 52 %.

Thyroid calorigenesis in isolated, perfused rat liver: minor role of active sodium‐potassium transport.

“…On the other hand, experiments with blood-perfused hind limbs of the cat had shown that only 5-6 % of the metabolic rate was expended for active Na-K transport under basal conditions (Crone, 1966). The same contribution (5-6 %) was found by Chinet, Clausen & Girardier (1977) in experiments with superfused, whole soleus muscle of the rat. Calculation from available results (Claret & Mazet, 1972;Claret, Claret & Mazet, 1973;Folke, 1974) suggested to us that the energy demand of active Na-K transport in the isolated, perfused liver of normal rats may also be relatively small.…”

“…I I THYROID CALORIGENESIS IN ISOLATED LIVER 413 question whether the presence of ouabain, while decreasing the rate of active Na-K transport, might also in some manner lead to increased energy utilization by other pathways (Chinet et al 1977). In the following section we have tried to elucidate the energy costs of ouabain-sensitive Na-K transport by applying available information about the stoichiometry of the Na-K-ATPase reaction to an estimate of ouabain-inhibitable ion fluxes derived from the results in Fig.…”

Ca(2+)‐dependent heat production by rat skeletal muscle in hypertonic media depends on Na(+)‐Cl‐ co‐transport stimulation.

“…The calorimetric signal, proportional to total heat production rate (E) of a soleus inuscle, was equal to the voltage difference between two series of six thermal gradient layers surrounding test and control chambers of a twini apparatus (for details, see Chinet, Clausen & Girardier, 1977), minus a blank difference (close to zero) which was recorded before introduction of the muscle into the test chamber. The proportionality constant between this signal and E was determined at various perfusion flow rates usinlg a calibrated field-effect transistor as the heat source.…”

Ca(2+)‐dependent heat production under basal and near‐basal conditions in the mouse soleus muscle.

“…The calorimetric signal, proportional to total heat production rate (E) by a pair of soleus muscles (12-26 mg wet weight measured at the end of the experiment after removal of the four tendons and rapid blotting on filter paper), was equal to the voltage difference between two series of six thermal gradient layers surrounding test and control chambers of a twin apparatus (for details, see Chinet, Clausen & Girardier, 1977) minus a blank difference, close to zero, which was recorded before the introduction of the muscles into the test chamber. The proportionality constant between this signal and E was determined at various perfusion flow rates using a calibrated field-effect transistor as the heat source.…”