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Biomedical subjects

D R Simpson

Publications and source records attributed to D R Simpson.

33 records · Page 2Linked to original sources
PubMed1977

A role for asparaginyl-tRNA in the regulation of asparagine synthetase in a mammalian cell line.

The expression of asparagine synthetase activity [L-aspartate:ammonia ligase (AMP-forming), EC 6.3.1.1] in cultured Chinese hamster ovary (CHO) cells is regulated by asparagine. After transfer of CHO cells from an asparagine-supplemented medium to a medium lacking asparagine, activity increases 1.5- to 2-fold. If asparagine is added back to the medium, activity returns to control levels. To test the possible involvement of Asn-tRNAAsn in regulating the levels of asparagine synthetase, we have examined the levels of asparagine synthetase in a mutant of CHO cells containing a temperature-sensitive asparaginyl-tRNA synthetase [L-asparagine:tRNA ligase (AMP-forming), EC 6.1.1.22]. Under conditions of limited asparaginyl-tRNA synthetase activity in the mutant, there is a 2- to 3-fold increase in the level of asparagine synthetase activity. Under identical conditions, there is no change in asparagine synthetase activity in the wild type. This correlation between asparaginyl-tRNA synthetase activity and asparagine synthetase levels may be a consequence of a direct role of tRNAAsn in the regulation of the in vivo expression of the asparagine synthetase structural gene.

Asparagine↗
PubMed1976

Histological and histochemical comparisons of muscle spindles in three hind limb muscles of the guinea pig.

Guinea pig soleus, medial gastrocnemius and vastus lateralis muscles were compared for spindle density and distribution, number of intrafusal fibers per spindle and histochemical appearance of the axial bundle. A total of 326 spindles was used in the comparisons. Spindle density was over four times greater in the soleus than in either the medial gastrocnemius or vastus lateralis. In the soleus the spindles were distributed at random, but in the other two muscles no spindles were found in those fascicles in which fast-twitch glycolytic extrafusal fibers predominated. The average number of intrafusal fibers per spindle varied by less than 5% between the three kinds of muscles. About 80% of all spindles located had four intrafusal fibers, two of the nuclear bag type and two of the nuclear chain type. The histochemical appearance of the axial bundle was the same in each kind of muscle. Based on intensities of the myofibrillar adenosine triphosphatase reaction product at polar regions nuclear bag fibers were separable into two histochemical groups; nuclear chain fibers were of only one histochemical type.

Adenosine Triphosphatases↗
PubMed1976

Properties of immobilized guinea pig hindlimb muscles.

Guinea pig hindlimbs were unilaterally immobilized at resting length to evaluate histochemical, biochemical, and contractile properties of immobilized muscle. Contralateral limbs remained unrestrained. Four weeks later contractile properties were measured under chloral hydrate anesthesia. Average time-to-peak tension of the immobilized soleus was 30% less, whereas that of the gastrocnemius was not significantly changed relative to contralateral muscles. Immobilized soleus muscles acquired as much as 25% fibers with high alkaline myofibrillar adenosine triphosphatase activity; these fibers do not occur in the normal muscle. Neither the immobilized soleus nor gastrocnemius fatigued more quickly than their contralateral counterparts. In the immobilized gastrocnemius myofibrillar protein (mg/g muscle) decreased to 76% and maximum tetanic tension to 70% of contralateral values. However, tetanic tension per gram wet muscle weight or 100 mg myofibrillar protein was significantly greater in the immobilized gastrocnemius. No specific factor responsible for the increased tetanic tension could be identified.

Adenosine Triphosphatases↗
PubMed1975

Muscle fibre type populations of human leg muscles.

Four selected leg muscles (gastrocnemius, soleus, vastus lateralis and intermedius) from thirty-two humans were autopsied within 25 hr of death and examined histochemically. The results of histochemical myofibrillar adenosine triphosphatase activity demonstrated that the soleus and vastus intermedius muscles have a higher proportion of slow twitch fibres (70%, 47%) than their synergists, gastrocnemius and vastus lateralis, respectively. The gastrocnemius contains about 50% slow twitch fibres and the vastus lateralis about 32%. Similar proportions of slow and fast twitch fibres have been reported for these hindlimb muscles in other mammals. Human muscles, however, differ from other mammalian muscles in that the proportion of slow and fast twitch fibres were similar in the superficial and deep regions of the muscles examined. Fast twitch oxidative glycolytic fibres in sedentary humans were observed less frequently, and they are less prominent in terms ofoxidative enzymatic activity when compared to similar fibres of several laboratory mammals studied previously.

Adenosine Triphosphatases↗
PubMed1974

Motor unit recruitment as reflected by muscle fibre glycogen loss in a prosimian (bushbaby) after running and jumping.

A qualitative histochemical assessment of glycogen loss in biopsies was made in bush-babies after running and jumping. Glycogen loss was related to the specific type of exercise. After running, glycogen loss was greatest in the slow-twitch oxidative fibre and depletion in the fast-twitch oxidative glycolytic fibres was similarly greater than in the fast-twitch glycolytic fibres. After jumping, the opposite pattern of glycogen utilization occurred (FG>FOG>SO).

Adenosine Triphosphatases↗