Biomedical subjects

M Walton

Publications and source records attributed to M Walton.

At least 91 records · Page 5Linked to original sources

PubMed1979

The relation of Vmax to INa, GNa, and h infinity in a model of the cardiac Purkinje fiber.

The inward sodium current in cardiac muscle is difficult to study by voltage clamp methods, so various indirect experimental measures have been used to obtain insight into its characteristics. These methods depend on the relationship between maximal upstroke velocity of the action potential (Vmax) and the sodium current (INa), usually defined in terms of the Hodgkin-Huxley model. These relationships were explored using an adaptation of this model to cardiac Purkinje fibers. In general Vmax corresponded to INa, and it could be used to determine the relationship of membrane potential to GNa, and h infinity. The results, however, depended on the method of stimulation of the action potential, and an optimal stimulation method was determined. A commonly used experimental technique called "membrane responsiveness" was shown to distort seriously the properties of steady-state gating inactivation that is supposed to measure. Estimation of the changes in maximal sodium conductance, such as those produced by tetrodotoxin (TTX), would be accurately measured. Some experimental results have indicated a voltage-dependent effect of TTX. Characteristics of the measures of TTX effect under those conditions were illustrated. In summary, calculations with a model of the cardiac Purkinje fiber action potential provide insight into the accuracy of certain experimental methods using maximal upstroke velocity as a measure of INa, and cast doubt on other experimental methods, such as membrane responsiveness.

Action Potentials↗

PubMed1979

Obesity as an aetiological factor in the development of osteoarthrosis.

A quantitative survey was carried out on the subcutaneous and abdominal adipose tissue of two inbred strains of mouse; STR/ORT is a strain in which the knee joints of the males have a very high incidence of osteoarthrosis, whereas the incidence of the disease in the females is much lower; the CBA/ORT mice represent a normal laboratory strain which rarely suffers from osteoarthrosis. In terms of the weight of readily removable subcutaneous and abdominal adipose tissue, the male STR/ORT mice were slightly leaner than the male CBA/ORT mice, the female STR/ORT mice were obese when compared with their CBA/ORT counterparts. Thus, in these mice, there was no positive correlation between obesity and osteoarthrosis. This evidence confirms previous mouse studies and is contrary to the commonly held view that in humans obesity predisposes to osteoarthrosis.

Adipose Tissue↗

PubMed1979

Bone thickening in osteoarthrosis. Observations of an osteoarthrosis-prone strain of mouse.

Estimations were made of the amount of bone (histologically) and the rate of bone formation (85Sr incorporation) in the epiphyses of the knees of osteoarthrosis-prone (STR/ORT) and normal (CBA/ORT) mice. Though the bone was significantly thicker in the STR/ORT mice, this was not the cause of the articular degeneration. Bone sclerosis and cartilage breakdown were chronologically very closely related with perhaps the cartilage changes occurring initially. In male STR/ORT mice bone formation was depressed in the cancellous bone of the epiphyses as, unlike the normal mice, it was at the same level as the compact bone of the femoral shaft. As there was no elevation of the osteoblastic activity in knee joints with developing osteoarthrosis, it would appear that bone sclerosis associated with the disease was due to decreased osteoclasis.

Animals↗

PubMed1978

Community nursing: how dependent are stroke patients?

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Activities of Daily Living↗

PubMed1978

A spontaneous ankle deformity in an inbred strain of mouse.

A spontaneous subluxation and subsequent dislocation of the bones of the ankle has been described in the males of an inbred strain of mouse (STR/ORT). It consisted of a gradual elevation of the calcaneum which eventually came to lie along the distal end of the tibia after 6--8 mth. The astragalus rotated forward. Articulations with the navicular and tarsal bones were severely disrupted with the accompanying development of peri-articular calcifications and ossifications. With one exception the arthropathy only occurred in male mice. Of the male members of the colony over the age of 3 mth, 26.7 per cent. had at least one ankle affected. Possible aetiological factors are discussed.

Animals↗

PubMed1977

Degenerative joint disease in the mouse knee; radiological and morphological observations.

Gross anatomical and radioligical techniques have been used to investigate the form and incidence of degenerative joint disease in the knee joint of an inbred strain of mouse (STR/ORT). The disease was seen radiographically as a thickening of the subchondral bone in the medial tibial and femoral condyles predominantly in the males. In fresh and macerated joints only advanced lesions could be seen with light microscopy and these appeared as concave (tibial) or flattened (femoral) erosions with hard shiny eburnated surfaces. Medial patella dislocation was a common feature of the arthrotic joints and there was associated widespread periarticular heterotopic calcification. These growths started as peripheral exostoses from the patella and as small loci of mineralisation within the synovial tissue but later enlarged into plaques of calcified tissue. Ossific centres within the menisci were present in all knees but became greatly enlarged in the osteoarthrotic joints. Calcification of the collateral ligaments occurred in non-arthrotic joints, especially laterally, but progressed to thick ossification in the medial ligament of arthrotic knees. Eventually all these enlarging sites of calcification and ossification began to fuse together, thus limiting the degree of movement of the joint. There was a statistically significant positive relationship between the severe arthropathy and (a) marked patella dislocation and (b) the presence of calcification in the medial collateral ligament.

Aging↗

PubMed1977

Degenerative joint disease in the mouse knee; histological observations.

The knee joints from males of two strains (CBA/ORT and STR/ORT) were studied histologically. The incidence of degenerative joint disease was very high in the STR/ORT strain. Degeneration of the cartilage invariably occurred first at the interface of the cruciate ligament and articular cartilage of the tibia. Lesions were only seen on the medial tibial and later the medial femoral condyles. Blocks of fibrillated, uncalcified cartilage were gradually lost across the condyle, leaving the tidemark as a secondary articulating surface. Meanwhile the subchondral bone thickened and erosion continued through the calcified cartilage into the underlying bone. A statistically significant relationship was found between the development of the lesion and (a) medial dislocation of the patella, (b) calcification and ossification of the medial collateral ligament. Patella dislocation gave rise to extensive cartilaginous and bony metaplasia of the synovial tissue. In joints with advanced degeneration there was often evidence of a slight lateral subluxation of the femur relative to the tibia.

Aging↗

PubMed1977