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Biomedical subjects

A R Khan

Publications and source records attributed to A R Khan.

At least 109 records · Page 6Linked to original sources
PubMed1980

Mechanism of action of pentobarbital on the contractile system of isolated frog muscle fibres.

The effects of pentobarbital-sodium were studied on single muscle fibres of frog skeletal muscle. In a concentration of 0.5 mM, pentobarbital potentiated the twitch response without significantly affecting the tetanus amplitude. The increase in twitch amplitude was accompanied by a marked increase in the rate of force development. The relaxation phase of both twitch and tetanus was prolonged. These mechanical changes were associated with an increased duration of the action potential. Pentobarbital also increased the amplitude and the rate of force development during the twitch after suppression by dantrolene. The S-shaped curve relating peak contracture tension and log caffeine concentration was shifted to the left by pentobarbital. It is suggested that pentobarbital affects the contractile activity of the muscle fibre; (1) by increasing the rate of release of calcium from its storage sites, (2) by prolonging the duration of the action potential and (3) by inhibiting calcium resequestration by the sarcoplasmic reticulum (SR).

Action Potentials↗
PubMed1980

Comparison of 133Xe single-breath and washout imaging in the scintigraphic diagnosis of pulmonary embolism.

To compare the utility of 133Xe single-breath (SB) and prolonged washout (WO) imaging in the scintigraphic diagnosis of pulmonary embolism, ventilation and perfusion studies of 66 patients who had pulmonary angiography within 48 hours were reviewed. The single-breath-perfusion (SB-P) and washout-perfusion (WO-P) studies agreed in 59 of 66 patients (89%). Each of the seven patients with disparate interpretations had an SB-P interpretation with a high probability for pulmonary embolism and a WO-p reading of low probability, with 133Xe retention in areas which appeared normal on the SB image. Single-breath images with 133Xe are not suitable as the sole determinant of ventilation-perfusion (V-P) match or mismatch, especially when subsegmental perfusion defects are present. Prolonged washout imaging improves the specificity of V-P imaging in patients with suspected pulmonary embolism.

Adult↗
PubMed1980

Studies on the breeding habitats and seasonal prevalence of larval population of Aedes aegypti (L.) and Aedes albopictus (skuse) in Dacca city.

An one-year study was conducted on the outdoor breeding habitats and seasonal prevalence of larval populations of Aedes aegypti and Aedes albopictus in ten different locations of Dacca city. Nine locations were found infested with larvae of either one or both species during the rainy season (May to October) of the year. A total of 1898 containers/sites were surveyed out of which 86 (4.53%) were infested with either one or both species. Out of then different kinds of artificial containers and natural habitats surveyed, Ae. albopictus larvae were present in nine including all four natural sites resulting in highest number and per cent (54, 62.8%) of albopictus infested container in the city. Ae aegypti larvae were present in only four kinds of artificial containers. Earthen pot was the most numerous breeding habitat (24.3%, 461) and contributed the highest number of infested container (45.3%, 39) Seasonal variations in the larval population of both species closely followed the fluctuations in rainfall with zero population during the driest three months.

Aedes↗
PubMed1979

Effects of 4-aminopyridine on the excitation-contraction coupling in frog and rat skeletal muscle.

The effects of 4-aminopyridine (4-AP) were studied on isolated single muscle fibres of the frog and toe muscles of the rat. In both muscle preparations, 4-AP potentiated the twitch amplitude without significantly affecting the tetanus response. There was an increase of the time to peak tension and, in frog muscle, an increased time to half relaxation. 4-AP produced no change of the resting membrane potential. The rate of decay and, hence, the total duration of the action potential were markedly prolonged. 4-AP did not induce contractures by itself nor did it affect the contracture induced by caffeine. The mechanical threshold was determined by measuring the contracture response to various degrees of depolarization by potassium. This threshold was not affected by 4-AP. Twitch potentiation by 4-AP was independent of the extracellular calcium concentration. It is concluded that 4-AP potentiates the twitch response by increasing the release of activator calcium into the myofibrillar space by prolongation of the action potential. In addition, there may be a more direct inhibitory action of 4-AP on the calcium re-uptake by the sarcoplasmic reticulum in frog muscle.

Action Potentials↗
PubMed1979

Effects of diethyl-stilboestrol on single fibres of frog skeletal muscle.

The effects of diethyl-stilboestrol (DES), one of the most potent estrogens, were studied on single muscle fibres of the frog. In relatively low concentrations (5 muM), DES greatly potentiates the twitch response of the fibre without significantly affecting the amplitude of the tetanus response. The twitch potentiation is accompanied by an increase in time to peak tension and marked prolongation of the relaxation phase. In tetanic response the half decay time after the last stimulus is also prolonged by DES. DES causes no changes in the resting or action potential of the muscle fibre. The S-shaped curve relating peak contracture tension and caffeine concentration is shifted towards lower caffeine concentrations by DES. Dantrolene greatly suppresses the DES potentiated twitch. It is concluded that DES potentiates the twitch response and prolongs the relaxation time by inhibition of the calcium re-uptake by the sarcoplasmic reticulum.

Action Potentials↗
PubMed1978

Disease agents carried by flies in Dacca city.

Studies were conducted to determine the different disease agents naturally carried by flies in Dacca city by collecting outdoor unbaited flies from 8 different representative locations and identifying the agents in the laboratory. Out of 96 fly pools containing 25 flies each, 62.5%, 46.9%, 15.6%, 8.3%, 8.3%, 15.6% and 6.2% of the pools were found positive for Ascaris lumbrioeides, Trichuris trichiura, Hookworm, Enterebious vermicularis eggs and Entamoeba coli, Trichomonas spp Giardia spp. cysts, respectively. Similarly, out of the same number of fly pools, 8.3%, 6.25%, 66.6%, 20.8% and 29.2% of the pools were found positive for Shigella flexner-3, Cholera vibrio, Escherichia coli, Staphylococcus aureus and Pseudomonas, respectively besides many other non-pathogenic bacteria.

Animals↗