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Biomedical subjects

X Holy

Publications and source records attributed to X Holy.

30 records · Page 2Linked to original sources
PubMed1993

Skeletal unloading in rat decreases proliferation of rat bone and marrow-derived osteoblastic cells.

The effects of skeletal unloading on osteoblastic cells were evaluated in tail-suspended rats. Hindlimb elevation for 14 days induced osteopenia, decreased histomorphometric indexes of bone formation in tibial metaphysis, and reduced plasma osteocalcin and alkaline phosphatase (ALP) levels compared with controls. The in vitro proliferation of osteoblastic cells isolated from the endosteal bone surface of suspended tibias was decreased by 42 and 31% at 2 and 4 days of culture, respectively, compared with controls, as shown by [3H]thymidine labeling and cell number. The proliferation of ALP-positive marrow stromal cells was also decreased by 20-24% at 1 and 2 days of culture. However, ALP activity in bone-derived cells and marrow stromal cells was not different in unloaded and control rats, and the number of bone cells synthesizing osteocalcin, osteonectin, and type I or type III collagen was identical in the two groups. The results indicate that the inhibition of bone formation induced by skeletal unloading is related to a decreased proliferation of putative osteoblast precursor cells present along the endosteal bone surface and in the marrow stroma.

Alkaline Phosphatase↗
PubMed1993

Functional adaptation of different rat skeletal muscles to weightlessness.

The adaptation to weightlessness of two postural muscles, the slow soleus (SOL) and the fast gastrocnemius lateralis (GL), and a fast muscle used in movements, the extensor digitorum longus (EDL), was studied on five adult Wistar rats. The animals exposed to 14-day spaceflight aboard COSMOS 2044, designated as flight (F), were compared with synchronous (S) animals. The experiments were performed on single skinned fibers whose functional properties were studied. After weightlessness, the SOL exhibited two populations of fibers according to their Sr2+ affinities: 40% remained slow (Fs) and 60% acquired fast-type properties (Ff). Both S and F GL and EDL showed a single distributed population of fast fibers. SOL fibers atrophied insofar as they showed a significant reduction in fiber diameter and absolute maximal tension Po (mg) but not in Po expressed in kg/cm2. GL fibers showed no change in fiber diameter but a decrease in Po in mg and kg/cm2. EDL fibers were not atrophied by weightlessness. The tension/Ca concentration relationships of the Ff SOL and F GL fibers were shifted to the right, indicating a decrease in their Ca2+ affinity. An increase in the contraction kinetics was described for the SOL fibers after weightlessness, whereas no significant modification was found for the GL and EDL. Collectively, the data suggested that the adaptive changes subsequent to weightlessness were more dependent on the muscle function than on the fiber type, since both postural SOL and GL were modified.

Adaptation, Physiological↗
PubMed1991

Effects of short spaceflights on mechanical characteristics of rat muscles.

The aim of this study was to investigate the contractile protein characteristics after 5-day (Cosmos 1514) and 7-day (Cosmos 1667) spaceflights. The experiments were performed on skinned fibers from the soleus, gastrocnemius lateralis, and plantaris muscles isolated from Wistar rats. A reduction in fiber diameter might explain the decrease in the maximal tension in the soleus, whereas this tension was unaltered in the gastrocnemius and the plantaris. Moreover the calcium sensitivity of the myofilament appeared modified in the soleus and in the gastrocnemius: The tension/pCa relationships were shifted toward higher calcium concentrations, indicating a decrease in the apparent calcium binding constant of the troponin C. The tension/pCa relationship appeared unaltered in the plantaris after spaceflight. Finally, the studies of the time to reach a steady tension indicated an increase in the rate of force development in the soleus and, on the contrary, a slowing down in the plantaris. No change in the gastrocnemius was found. The results were analyzed with references to the different muscle functions in disuse atrophy.

Animals↗
PubMed1990

Contractile properties of rat soleus muscle after 15 days of hindlimb suspension.

The properties of the contractile elements interacting to develop force in atrophied rat soleus muscle were studied by using single skinned fibers, which permitted direct access to the contractile apparatus. Muscle atrophy was induced by 15 days of hindlimb suspension. Suspension resulted in a decrease of maximal tension relative to an important decline in fiber diameter. Ca affinity of the contractile proteins was not changed insofar as the tension-pCa relationship was not shifted along the pCa axis. However, after hindlimb suspension 1) the value of the Hill coefficient from the tension-pCa curve was found to be higher, 2) a higher Ca threshold for activation was reported, and 3) a significant increase in contraction kinetics was described. All these results suggested that after suspension the mechanical properties of the slow-twitch soleus appeared to resemble more closely those of a fast-twitch muscle. Our results were in complete agreement with published histochemical data.

Animals↗
PubMed1989

Compared properties of the contractile system of skinned slow and fast rat muscle fibres.

Chemically skinned fibres from soleus and plantaris rat muscles were used to compare the contractile properties of slow and fast muscles. The maximal isometric tension appeared larger in plantaris than in soleus fibres. The apparent Ca2+ threshold for activation was lower in slow than in fast fibres while Ca2+ concentrations required to obtain either the maximal tension or half maximal tension (pCa50) were lower in fast than in slow fibres. This apparent difference in Ca2+ sensitivity will be discussed. As could be expected from other studies, a faster force development in plantaris than in soleus fibres occurred. However, one interesting new result showed that in soleus, the kinetics of the tension development estimated by the tmax parameters were slightly dependent on the Ca2+ concentration whereas the t50 parameter changed significantly with the Ca2+ concentration. In plantaris, both tmax and t50 parameters were found to depend strongly on the Ca2+ concentration. Finally, the plantaris muscle showed a greater caffeine sensitivity than the soleus muscle. All the results suggested that the Ca-regulatory mechanism in the slow fibres was essentially different from that in the fast fibres.

Animals↗
PubMed1986

[Behavior of contractile proteins of rat muscle fibers under microgravity conditions].

Microgravity effects were studied on three muscles: gastrocnemius lateralis, plantaris and diaphragm, after the biocosmos 1514 and 1667 space flights. Results showed a decrease of maximal mechanical activity on both gastrocnemius and plantaris while no modification was observed on diaphragm. Cross-bridge cycling speed was reduced on both gastrocnemius and plantaris. Moreover, a reduced calcium binding affinity appeared in gastrocnemius.

Animals↗
PubMed1984

Intramuscular calcium movements: experiments from the Soviet biosatellite Biocosmos.

Experiments have been performed in skeletal muscle fibres from the lateral head of gastrocnemius muscle of female rats. Changes in intramuscular calcium movements due to microgravity conditions have been tested by tension measurements in chemically skinned muscle fibres. Our results show that microgravity induces i) a decrease in maximal muscle strength developed by contractile proteins ii) a decrease of intensity and rate of both Ca release and Ca uptake by the sarcoplasmic reticulum.

Animals↗