High energy phosphate utilization for work production and tension maintenance in frog muscle

Frog (Rana esculenta, L.) gastrocnemii (161 pairs) or sartorii (8 pairs) were stimulated by intermittent tetani at 10°C (20 Hz, supramaximal intensity, N₂ atmosphere) isometrically (IM) or isotonically (IT) for various durations (6–30 s) at different tensions (0.05–1.00 P₀=maximal IM tension at resting length,l _o). The energy expenditure (E) was measured from ATP and phosphocreatine breakdown and the high energy phosphate equivalent of lactic acid production. Both in IM and IT conditions,E was found to be a linear function of the summated tetanus duration (t):E=a+b t, whereb is the energy cost of tension maintenance. For the gastrocnemius, both in IM and IT,b was independent of the tension developed and equal to 0.45 mol P · g^–1 · s^–1, whereas for the sartoriusb was tension-dependent, varying between 0.58 and 0.28 mol P · g^–1 · s^–1 for P₀ and 0.18 P₀, respectively. The constancy of theb value in muscles with pennate structure may be tentatively attributed, at least in part, to the greater internal energy dissipation, regardless of the tension developed. The terma of the above equation is due to all time-independent processes of muscle contraction, i.e.: (1) activation energy; (2) internal work and (3) external work (in IT only). Based on the measured value ofa and on the work performed, the mechanical equivalent of P splitting was calculated as 17.7 kJ · mol^–1, a figure close to that previously obtained on frog sartorius (16.7 kJ · mol^–1) and dog gastrocnemius (19.2 kJ · mol^–1) When taking into account the energy due to the activation processes, the calculated net mechanical equivalent of P splitting amounted to 25.5 kJ · mol^–1.     

An energy balance of front crawl

With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C= v^–1, where is the metabolic power and v is the speed) and the overall efficiency (_o=W_tot/C, where W_tot is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W_tot is given by the sum of: (1) W_int, the internal work, which was calculated from video analysis, (2) W_d, the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W_k, calculated from measures of Froude efficiency (_F). In turn, _F=W_d/(W_d+W_k) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s^–1, _F is about 0.5, power to overcome water resistance (active body drag × v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds increases from 600 to 1,200 W and C from 600 to 800 J m^–1. The use of fins decreases total mechanical power and C by the same amount (10–15%) so that _o (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of _o are higher than previously reported for the front crawl, essentially because of the larger values of W_tot calculated in this study. This is so because the contribution of W_int to W_tot was taken into account, and because _F was computed by also taking into account the contribution of the legs to forward propulsion.     

Lung preservation solution substrate composition affects rat lung oxidative metabolism during hypothermic storage

Lungs harvested for transplantation utilize oxygen after procurement. We investigated the effects of storage solution substrate composition on pulmonary oxidative metabolism and energetics during the preservation interval. Rat lungs were harvested and stored at 10 degrees C in low-potassium dextran (LPD) solution. Groups of lungs were preserved with preservation solution containing 5mM carbon-13 ((13)C) labeled glucose or increasing concentrations of (13)C labeled pyruvate. Additional groups of rat lungs were studied with dichloroacetate (DCA) added to the pyruvate-modified preservation solutions. Oxidative metabolism (measured by (13)C-enrichment of glutamate) and adenine nucleotide levels were quantified. Increasing preservation solution pyruvate concentration augmented glutamate (13)C-enrichment up to a concentration of 32mM pyruvate. DCA further stimulated oxidative metabolism only at lower concentrations of pyruvate (4 and 8mM). ATP and ADP were not different among groups, but AMP levels were higher in the glucose group. These data suggest that altering the substrate composition of the preservation solution influences lung metabolism during allograft preservation for transplantation.     

Temperature and the energy cost of oscillatory work in teleost fast muscle fibres

Bundles of 20–30 fast muscle fibres were isolated from the abdominal myotomes of the short-horned sculpin (Myoxocephalus scorpius L.). The energy cost of contraction was measured during oscillatory work at 4 °C and 15 °C following treatment with iodoacetate and nitrogen gas to block glycolysis and aerobic metabolism. Isolated fibres were subjected to sinusoidal length changes about in situ resting length and stimulated at a selected phase in the strain cycle. Preliminary experiments with untreated preparations established the strain amplitude and stimulation parameters required to maximize work output over a range of cycle frequencies at 4 °C and 15 °C. Following oscillatory work, treated preparations were rapidly frozen, freeze-dried and the concentrations of phosphocreatine (PCr), creatine, adenosine 5-triphosphate (ATP), adenosine 5- di- and mono-phosphate and inosine 5-monophosphate measured by high performance liquid chromatography. The concentration of PCr declined in proportion to the total work done for up to 64 cycles without a significant change in ATP. Maximum power output was produced at a cycle frequency of 5 Hz at 4 °C (14–18 W/kg) and 17 Hz at 15 °C (23–27 W/kg). The rate of utilization of PCr per cycle was independent of temperature. However, since work per cycle was higher at 4 °C (2.7–3.7 mJ/g wet weight) than 15 °C (1.2–1.6 mJ/g wet weight), the energetic cost of contraction decreased with increasing temperature.     

Advances in understanding the molecular basis of the first steps in color vision

Serving as one of our primary environmental inputs, vision is the most sophisticated sensory system in humans. Here, we present recent findings derived from energetics, genetics and physiology that provide a more advanced understanding of color perception in mammals. Energetics of cis–trans isomerization of 11-cis-retinal accounts for color perception in the narrow region of the electromagnetic spectrum and how human eyes can absorb light in the near infrared (IR) range. Structural homology models of visual pigments reveal complex interactions of the protein moieties with the light sensitive chromophore 11-cis-retinal and that certain color blinding mutations impair secondary structural elements of these G protein-coupled receptors (GPCRs). Finally, we identify unsolved critical aspects of color tuning that require future investigation.     

Calbindin overexpression buffers hippocampal cultures from the energetic impairments caused by glutamate

A dramatic rise in free cytosolic calcium concentration is thought to be a central event in the pathogenesis of glutamate excitotoxicity in neurons. We have previously demonstrated that gene transfer of the calcium-binding protein calbindin D28k via a Herpes simplex amplicon vector decreases the rise in intracellular calcium and promotes cell survival following glutamatergic challenge. This study explores the effect of calbindin transgene expression on cellular metabolism following glutamate excitotoxicity. Because excitotoxic insults are often energetic in nature, and because calcium sequestering and extrusion place heavy energy demands on a cell, we hypothesized that calbindin overexpression may help preserve cellular energy levels during an insult. We overexpressed calbindin in primary hippocampal cultures, using a Herpes simplex amplicon vector system. We found that calbindin overexpression protected neurons from the decline in ATP levels, mitochondrial potential and metabolic rate following a glutamatergic insult. These results indicate that calbindin expression helps preserve cellular energy state following glutamate excitotoxicity. This illustrates the energetic load placed on neurons by increased free cytosolic calcium and may help explain the neuroprotective effects of calbindin.     

Muscle efficiency: the controversial role of elasticity and mechanical energy conversion in stretch-shortening cycles

The analysis of muscle efficiency was performed on a variety of simulated muscle stretch-shortening cycles of in situ rat gastrocnemius muscle. The processes of biochemical energy conversions (phosphorylation and contraction-coupling) and mechanical conversions (internal work to external work) were incorporated in the efficiency calculations. Metabolic cost was determined using a simple linear model. Special attention was drawn to the interacting roles of series elastic compliance and contraction dynamics. The results showed that series elastic compliance affected the efficiency of muscle contraction to a great extent. Stiff muscle was well designed to perform efficient contractions in which muscle merely shortened while active. Compliant muscle performed best in true stretch-shortening contractions utilising the storage and release of series elastic energy effectively. However, both stiff and compliant series elastic elements showed similar optimal muscle efficiency values in shortening contractions and stretch-shortening contractions, respectively. The findings indicate that the storage and re-utilisation of series elastic energy does not enhance overall muscle efficiency, but that optimal efficiency is obtained by a proper design of the muscle with regard to the dynamics of the movement task. Furthermore, it was found that although biochemical efficiency determined the feasible range of muscle efficiency, mechanical work conversions had the strongest influence on the exact value of overall muscle efficiency in stretch-shortening contractions. Electronic Publication     

Costs of pair-bonding and paternal care in male prairie voles (Microtus ochrogaster)

The direct costs of paternal care are relatively well documented in primates, however little research has explored these effects in monogamous rodents. The present study examines the long-term effects that pairing and parenting have on male prairie voles. We hypothesized that there would be a significant weight loss over the course of pairing and parenting, presumably from the energetic demands that accompany these changes in social condition. In a longitudinal study, we followed ten male prairie voles through being housed with their brother; paired with a female; and caring for three consecutive litters. We found a significant drop in bodyweight across time, with maximum weight loss near the weaning of the first litter. At that same time, feeding increased, leading to possible recovery in weight; however, leptin levels dropped precipitously across time and did not recover. Corticosterone did not change significantly across time points, and overall activity levels also did not vary significantly over the course of the study. In addition, newly paired males showed a significant increase in preference for a 2% sucrose solution during a three-hour test, indicating a metabolic need for more calories. A cross-sectional study confirmed leptin and corticosterone findings, and showed significant loss of subcutaneous (inguinal) fat in males that had cared for a litter of pups, when compared to males housed with their brothers or newly paired males. These results suggest that cohabitation with a female, and caring for pups, all have costs for male prairie voles.     

Disopyramide improves the balance between myocardial oxygen supply and demand in patients with hypertrophic obstructive cardiomyopathy

Summary We evaluated the effects of disopyramide in terms of the balance between myocardial oxygen supply and demand in patients with hypertrophic obstructive cardiomyopathy (HOCM). The myocardial oxygen supply was evaluated by measuring coronary flow velocity and the myocardial oxygen demand was assessed by the pressure-volume area (PVA). The time velocity integral of coronary flow did not change significantly (20±6 to 21±8 cm), but the peak left ventricular pressure and left ventricular external work decreased significantly (206±44 to 157±37 mmHg,P<0.001; 1.09±0.33 to 0.80±0.23 J/beat,P<0.001) after disopyramide administration. From theoretical analysis using these data, we concluded that disopyramide improves the myocardial oxygen supply-demand balance in patients with HOCM.