Lactate as substrate for glycogen resynthesis after exercise

Muscle glycogen levels in the perfused rat hemicorpus preparation were reduced two-thirds by electrical stimulation plus exposure to epinephrine (10(-7) M) for 30 min. During the contraction period muscle lactate concentrations increased from a control level of 3.6 +/- 0.6 to a final value of 24.1 +/- 1.6 mumol/g muscle. To determine whether the lactate that had accumulated in muscle during contraction could be used to resynthesize glycogen, glycogen levels were determined after 1-3 h of recovery from the contraction period during which time the perfusion medium (flow-through system) contained low (1.3 mmol/l) or high (10.5 or 18 mmol/l) lactate concentrations but no glucose. With the low perfusate lactate concentration, muscle lactate levels declined to 7.2 +/- 0.8 mumol/g muscle by 3 h after the contraction period and muscle glycogen levels did not increase (1.28 +/- 0.07 at 3 h vs. 1.35 +/- 0.09 mg glucosyl U/g at end of exercise). Lactate disappearance from muscle was accounted for entirely by output into the venous effluent. With the high perfusate lactate concentrations, muscle lactate levels remained high (13.7 +/- 1.7 and 19.3 +/- 2.0 mumol/g) and glycogen levels increased by 1.11 and 0.86 mg glucosyl U/g, respectively, after 1 h of recovery from exercise. No more glycogen was synthesized when the recovery period was extended. Therefore, it appears that limited resynthesis of glycogen from lactate can occur after the contraction period but only when arterial lactate concentrations are high; otherwise the lactate that builds up in muscle during contraction will diffuse into the bloodstream.     

Improvements in exercise performance: effects of carbohydrate feedings and diet

In an effort to determine the effects of carbohydrate (CHO) feedings immediately before exercise in both the fasted and fed state, 10 well-trained male cyclists [maximum O2 consumption (VO2 max), 4.35 +/- 0.11 l/min)] performed 45 min of cycling at 77% VO2 max followed by a 15-min performance ride on an isokinetic cycle ergometer. After a 12-h fast, subjects ingested 45 g of liquid carbohydrate (LCHO), solid carbohydrate confectionery bar (SCHO), or placebo (P) 5 min before exercise. An additional trial was performed in which a high-CHO meal (200 g) taken 4 h before exercise was combined with a confectionery bar feeding (M + SCHO) immediately before the activity. At 10 min of exercise, serum glucose values were elevated by 18 and 24% during SCHO and LCHO, respectively, compared with P. At 0 and 45 min no significant differences were observed in muscle glycogen concentration or total use between the four trials. Total work produced during the final 15 min of exercise was significantly greater (P less than 0.05) during M + SCHO (194,735 +/- 9,448 N X m), compared with all other trials and significantly greater (P less than 0.05) during LCHO and SCHO (175,204 +/- 11,780 and 176,013 +/- 10,465 N X m, respectively) than trial P (159,143 +/- 11,407 N X m). These results suggest that, under conditions when CHO stores are less than optimal, exercise performance is enhanced with the ingestion of 45 g of CHO 5 min before 1 h of intense cycling.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of prostaglandin biosynthesis by human ovarian follicular fluid: a mechanism for ovulation?

We have studied the effect of human ovarian follicular fluid on PG production by bovine seminal vesicles in vitro and found that hFF1 contains a factor of high molecular weight (Mr greater than 30,000) which inhibits PG synthase in a dose-dependent manner. Exposure of this substance to protease activity produced a factor of lower molecular weight (Mr less than 1000) which stimulated PG synthase activity. If this is true of ovarian follicles in vivo, it is possible that increased follicular protease activity stimulates PG synthesis at the time of ovulation.     

An autoradiographic study of the uptake of tritiated proline by osteoblasts during hibernation

Twenty-four LSH and LVG strain golden hamsters, Mesocricetus auratus, were used. Experimental animals were maintained at 5 C and allowed to hibernate. Control animals were kept at 27 C. Six animals (3 experimental, 3 control) were injected subcutaneously with 1 microCi of 3H-proline/gm body wt. (Spec. act. 3 Ci/mM) after hibernation lasting 12 hours, 1 day, 3 days, or 7 days. Animals were killed 1 hour after injection and autoradiographs were prepared from 5 microns thick decalcified sections of femurs. A greater number of endosteal cells were labeled than periosteal cells and also exhibited a greater magnitude of labeling throughout the study. Differences between endosteal and periosteal cells both in percentage of cells labeled and magnitude of labeling were maximum in control animals and progressively decreased with increasing periods of hibernation. A reduction in synthesis of matrix proteins during the early period of hibernation was seen and was attributed to a significant reduction both in average cell activity and in the number of active cells during hibernation. The latter phenomenon apparently made a large contribution to the reduced matrical synthesis. 3H-proline uptake by osteoblasts probably reflects the reduced requirements of matrical synthesis during hibernation.     

Molecular hybridization to meiotic chromosomes in man reveals sequence arrangement on the no. 9 chromosome and provides clues to the nature of "parameres"

In situ hybridization of male human meiotic material has been used to elucidate the molecular organization of the centromeric region of human chromosome 9. The use of two cloned DNA sequences has shown that the centromere and the secondary constriction of this chromosome contain two separate repeated DNA families. The secondary constriction organizes into "paramere" bodies during pachytene. The individual parameres are comprised of one family of repeated DNA sequences.     

Effect of ion channel blockers on germination of Bacillus megaterium spores

Abstract We surveyed 23 drugs that can interact with membrane components, such as ion channels, for their effect on spore germination. The results showed that triggering of spore germination was inhibited by specific calcium (Ca²⁺) potassium (K⁺) and sodium (Na⁺) channel blockers.     

Protein-protein interactions in the 18S ATPase of Chlamydomonas outer dynein arms

When outer-row dynein arms are extracted from Chlamydomonas flagellar axonemes, they dissociate into two ATPase complexes with sedimentation coefficients of 12S and 18S. We immunized mice with 18S dynein and generated a library of monoclonal antibodies against the polypeptides in this complex. Antibodies were selected which specifically recognize the 18S alpha- and beta-heavy chains and the 83,000-dalton and 70,000-dalton intermediate chains. These antibodies were isolated and characterized for their ability to recognize determinants on both denatured antigens and native 18S dynein; 18S dynein was dissociated in stepwise fashion into smaller aggregates with ionic and nonionic detergents and the resulting subcomplexes were isolated by precipitation with specific monoclonal antibodies. The smallest aggregates isolated were heterodimers between the alpha-chain and a 16,000-dalton light chain and between the two intermediate chains. Additional close associations of the beta-heavy chain with an 18,000-dalton light chain and 70,000-dalton intermediate chain, and a weaker interaction between the intermediate chain heterodimer and light chains of 21,000 daltons and 12,500 daltons, were also observed. We present a model of 18S dynein substructure based upon this information.     

Enzymes of pyrimidine deoxyribonucleotide metabolism in Mycoplasma mycoides subsp. mycoides.

Cell-free extracts of Mycoplasma mycoides subsp. mycoides were assayed for enzymes associated with the salvage synthesis of pyrimidine deoxyribonucleotides. They possessed kinases for deoxycytidine, (d)CMP, thymidine (deoxyuridine), dTMP, and nucleoside diphosphates; dCTPase and dUTPase; dCMP deaminase; thymidine (deoxyuridine) phosphorylase; and dUMP (dTMP) phosphatase. The existence of these enzymic activities together with ribonucleoside diphosphate reductase explains the capacity of cytidine to provide M. mycoides with deoxyribose for the synthesis of thymidine nucleotides from thymine.     

Bleomycin treatment of chick fibroblasts causes an increase of polysomal type I procollagen mRNAs. Reversal of the bleomycin effect by dexamethasone

Bleomycin treatment of primary chick skin fibroblasts and chick lung fibroblasts resulted in a selective dose-dependent increase of cell layer procollagen synthesis. Solid support hybridization of total cellular RNA to 32P-labeled pro-alpha 1(I) and pro-alpha 2(I) cDNAs did not indicate an increase of total cellular procollagen type I mRNAs in bleomycin-treated cells. However, bleomycin treatment of chick skin fibroblasts causes a redistribution of procollagen type I mRNAs within the nuclear, cytoplasmic, and polysomal subcellular fractions. Both the nuclear and cytoplasmic procollagen type I mRNAs are significantly decreased in concentration after bleomycin administration. In contrast, the polysomal procollagen type I mRNAs are significantly increased in both chick skin and lung fibroblasts treated with bleomycin. Administration of dexamethasone to bleomycin-treated fibroblasts resulted in a reversal of the bleomycin-induced increase in cell layer procollagen synthesis. The increased amounts of polysomal procollagen type I mRNAs in bleomycin-treated cells were also reduced by subsequent administration of dexamethasone. These data indicate that bleomycin treatment of chick skin and chick lung fibroblasts results in a specific increase in procollagen synthesis in the cell layer which is mediated by elevated levels of polysomal type I procollagen mRNAs via a repartitioning of these mRNAs within the fibroblast. Furthermore, dexamethasone reverses the bleomycin-induced elevations of both cell layer procollagen synthesis and polysomal type I procollagen mRNAs.     

Morphology of isolated triads

The triad is the junctional association of transverse tubule with sarcoplasmic reticulum terminal cisternae. A procedure for the isolation of highly enriched triads from skeletal muscle has been described in the previous paper. In the present study, the structural features of isolated triads have been examined by thin-section, negative-staining, and freeze-fracture electron microscopy. In isolated triads, key features of the structure observed in situ have been retained, including the osmiophilic "feet," junctional structures between the transverse tubule and terminal cisternae. New insight into triad structure is obtained by negative staining, which also enables visualization of feet at the junctional face of the terminal cisternae, whereas smaller surface particles, characteristic of calcium pump protein, are not visualized there. Therefore, the junctional face is different from the remainder of the sarcoplasmic reticulum membrane. Junctional feet as viewed by thin section or negative staining have similar periodicity and extend approximately 100 A from the surface of the membrane. Freeze-fracture of isolated triads reveals blocklike structures associated with the membrane of the terminal cisternae at the junctional face, interjunctional connections between the terminal cisternae and t-tubule, and intragap particles. The intragap particles can be observed to be closely associated with the t-tubule. The structure of isolated triads is susceptible to osmotic and salt perturbation, and examples are given regarding differential effects on transverse tubules and terminal cisternae. Conditions that adversely affect morphology must be considered in experimentation with triads as well as in their preparation and handling.