Robert E. Davies

The Chemical Energetics of Muscle Contraction. II. The Chemistry, Efficiency and Power of Maximally Working Sartorius Muscles

Sartorius muscles from Rana pipiens were stretched and then stimulated electrically at 0°C whilst being allowed to shorten at constant predetermined velocities on a Levin-Wyman ergometer. The muscles developed tensions appropriate to their instantaneous lengths and velocities. A comparison with the unstimulated paired control muscle allowed measurements to be made of the changes in phosphate compounds during these maximally-working, constant-velocity contractions. In contractions lasting less than 1.5 s, no significant differences were found in the usage of adenosine triphosphate or production of inorganic phosphate, for the performance of a constant amount of work, in normal aerobic muscles, anaerobic muscles pretreated with iodoacetate to inhibit lactate production, or muscles pretreated with 2, 4-dinitrofluorobenzene so that adenosine triphosphate was the only energy source. In slow contractions lasting longer than 1.5 s allowance had to be made for myokinase and other enzymic reactions. The amount of external work done by the muscles, as a result of the hydrolysis of each mole of adenosine triphosphate, was found to be very dependent on velocity, being low at low and high speeds of shortening with a maximum below 1 muscle length/second. The free energy available per mole of adenosine triphosphate was calculated and the thermodynamic efficiency of the muscles was found to be high. On the basis of 10 kcal/mol adenosine triphosphate the overall efficiency was over 66 ± 6% at 2 cm/s in experiments with muscles pretreated with 2, 4-dinitrofluorobenzene. The amount of adenosine triphosphate used for processes other than mechanical work (mainly calcium pumping) was estimated to be about one quarter of the total. After allowance had been made for this the efficiency was found to be 98 ± 15% at a constant shortening velocity of 2 cm/s. Conversely, the minimum free energy available for doing external work from ATP hydrolysis under these conditions must be 9.8 ± 1.5 kcal/mol.

Municipal Waterborne Giardiasis: An Epidemiologic Investigation: Beavers Implicated As a Possible Reservoir

Abstract In March 1976, 128 persons in Camas, Washington, had laboratory-confirmed giardiasis. A questionnaire survey of 498 Camas residents revealed that 3.8% had clinical giardiasis, while none o...

ADENOSINE TRIPHOSPHATE: CHANGES IN MUSCLES DOING NEGATIVE WORK.

Frog sartorius muscles were isolated, treated with 1-fluoro-2, 4-dini-trobenzene at 0�C, then stimulated tetanically at the length in situ and stretched with a Levin-Wyman ergometer during stimulation. The normal adenosine triphosphate breakdown during the tetanus was reduced by about half during the forced stretch. The tension was increased by about 70 percent, but resynthesis of adenosine triphosphate did not occur. Thus, on the basis of A. V. Hills results, adenosine triphosphate is probably not the direct final energy source for muscular contraction, although it intimately participates in the process. The use of adenosine triphosphate during negative work was less than one-tenth that needed for positive work.

The chemical energetics of muscle contraction I. Activation heat, heat of shortening and ATP utilization for activation-relaxation processes

Measurements have been made of the changes in adenosine triphosphate and inorganic phosphate associated with activation and shortening in isolated sartorius muscles of Rana pipiens at 0°C. The muscles were pretreated with 2, 4-dinitrofluorobenzene to inhibit adenosine triphosphate: creatine phosphotransferase. When unloaded muscles were stimulated electrically, allowed to shorten fully and stay shortened during further stimulation, it was found that the usage of adenosine triphosphate (and production of inorganic phosphate) per pulse became less and less at greater rates of stimulation. The adenosine triphosphate usage per second reached a plateau and continued for a short while after the last pulse. This adenosine triphosphate is presumably used almost entirely for pumping calcium. Very little adenosine triphosphate was used per pulse by muscles in hypertonic solutions. These muscles passed normal action potentials but did not shorten or develop tension. Muscles which were re-extended after each of a series of almost completely unloaded shortenings had been completed used only the small amount of extra adenosine triphosphate needed for the little extra work done. Even the total breakdown of adenosine triphosphate was much too small to account for the heat of shortening, if this heat is assumed to be degraded free energy from adenosine triphosphate. Experiments were carried out according to Professor A. V. Hill’s ‘Further challenge to biochemists’. They showed that less adenosine triphosphate was used in the first 200 ms by a lightly loaded isotonic muscle than by an isometric muscle. Thus the heat of shortening, which is observed only while the muscle is shortening but not in the whole contraction-relaxation cycle, cannot be degraded free energy from adenosine triphosphate.

Adenosine triphosphate breakdown during a single isotonic twitch of frog sartorius muscle.

Abstract Recent work has shown that 1-fluoro 2,4 dinitro-benzene (FDNB) can inhibit creatine phosphoryltransferase in , situ in isolated frog muscle. This made possible the first direct demonstration of the breakdown of amounts of adenosine triphosphate (ATP) quantitatively sufficient to account for the work done in a single smooth tetanic contraction of electrically stimulated frog rectus abdominis muscle. (Cain and Davies 1962) However, this muscle is slow and does not show classical twitch responses, so experiments have now been carried out with the intensively studied sartorius muscle which is fast and can perform normal twitches as well as tetanic contractions.

Crossbridge attachment, resistance to stretch, and viscoelasticity in resting mammalian smooth muscle

There exist a calcium-dependent resistance to stretch in resting mammalian smooth muscle that is not caused by depolarization of the cell membrane or release of calcium from intracellulr sites. The similarity of the resistance to stretch in the resting state to that in rigor suggests that most, if not all, crossbridges are attached and thus able to resist stretch in noncontracting smooth muscles. When the muscle is stretched the breaking and subsequent reformation of links in nonstrained positions accounts for most of the so-called viscoelasticity, except at extreme lengths.

The absence of gastric urease in germ-free animals

Abstract 1. 1.Measurements were made of the urease (urea amidohydrolase, EC 3.5.1.5) content of the gastric mucosae of conventional, germ free, and fetal animals to test whether gastric urease arises from micro-organisms or is constitutive. 2. 2.Homogenates of gastric mucosae of conventional sheep, dogs, cats, rats, guinea pigs, and chickens; of germ-free rats, guinea pigs, chickens, dogs, cats, and pigs; and of fetal dogs, cats, rats, sheep, and humans were prepared and analyzed for urease activity. 3. 3.There was no urease in the gastric mucosae of the germ-free or fetal animals, although enzymic activity was usually found in the same tissue from their conventional adult counterparts, which had a wide range of enzymatic activity.

Energy metabolism of the renal medulla.

Abstract 1. 1. A study has been made of the rate of anaerobic glycolysis and of oxygen consumption by slices of the inner medulla and of the cortex of the dog kidney. The effects of increased osmolality of the medium by sodium chloride upon these processes have also been studied. 2. 2. With an osmolality of the medium of 300 mOsmole/kg water the Q CO 2 N 2 of the inner medulla was 5.1 ± 0.35 whereas that of the cortex was 1.4 ± 0.06. Cortical slices showed a progressive inhibition of the rate of glycolysis as osmalality was increased; inner medullary slices on the other hand showed no significant inhibition of glycolysis until osmolality was raised to 1100–1300 mOsmole/kg water. 3. 3. In contrast to the above, the cortex showed a higher Q 0 2 (−14.1 ± 0.072) than did the inner medulla (−2.26 ± 0.084) when the osmolality of the medium was 300 mOsmole/kg water. Increases in osmolality of the medium caused equal degrees of inhibition of the rate oxygen consumption by both cortical and inner medullary slices. 4. 4. Physiological considerations strongly suggest that the energy necessary for the metabolism of the renal medulla and hence for the countercurrent multiplier which resides in the structures of this region is derived from anaerobic pathways. The results of this study suggest that the renal medulla can operate an anaerobic metabolism under conditions which approach those present in vivo during antidiuresis.

Carnosine phosphate as phosphate donor in muscular contraction.

CARNOSINE phosphate was first synthesized by Severin, Georgievskaya and Ivanov1 by a method very similar in detail to that for creatine phosphate2. They showed that this method yields as a rule a diphosphate, both phosphate bonds being high-energy; but that the one which is not on the imidazole ring is more labile. In the presence of muscle extract the latter is transferred to adenosine diphosphate.

The role of phosphate compounds in thaw contraction and the mechanism of thaw rigor

Abstract 1. Frozen frog sartorius muscles, when thawed rapidly, contracted in 5 sec performing up to 300 g·cm external work per g muscle. The contraction was characterized by a release of Ca2+ and rapid utilization of ATP. 2. In muscles pre-treated with 0.38 mM FDNB in a bicarbonate saline solution the efficiency based on the total ATP used was 17.3 ± 1.8 g·m work per μmole (4% at −10 kcal per mole ATP being split to ADP). In addition to the actomyosin ATPase, the following enzyme systems were found to be active: adenylate kinase, adenylate deaminase and the formation of hexose monophosphates. ATP: creatine phosphotransferase was completely inhibited. The muscles went rapidly into rigor while much active tension was maintained. 3. In untreated aerobic muscles, the thaw contraction used ATP and phosphorylcreatine. This was followed by a phase of lengthening under the load and rigor developed only 20–30 min later at 24°. This pre-rigor phase was accompanied by increased levels of ADP. 4. When rigor developed (both FDNB-treated and untreated muscles) the sarcoplasmic level of ADP was very low. Thus, the development of rigor requires the absence of both ADP and ATP.