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Biomedical subjects

B D Gupta

Publications and source records attributed to B D Gupta.

At least 91 records · Page 5Linked to original sources
PubMed1981

Absorption of light in photoreceptors: transverse incidence.

The time variation of the absorption rate (i.e., the number of photons absorbed per see) in a photoreceptor when light is incident perpendicular to its axis has been studied for various species and different conditions. Due to the cylindrical geometry of the photoreceptor the expressions for the absorption rates become very complicated. Hence, simple approximate expressions for the absorption rates in the case of some of the species have been suggested. The present analysis will be useful in analysing the mechanism of the photoreceptor when light is incident perpendicular to the axis.

Animals↗
PubMed1980

Absorption of light in photoreceptors: effect of waveguiding property.

The effect of waveguiding property (i.e., the intensity distribution) of the photoreceptor on the number of photons absorbed in a photoreceptor has been studied. It has been found that the effect is significant only for large values of the exposure and the maximum effect is less than 11% in the case of human rod photoreceptor. In the analysis, the funnelling effect, which follows from the coupling between the interior and exterior fields, has not been considered.

Animals↗
PubMed1979

The directional absorption properties of rhodopsin and its photoproducts.

The experimental data on the absorption of a plane polarised light by a solution of cattle rhodopsin at -196 degrees C have been theoretically analysed to model the directional absorption properties of rhodopsin and its photoproducts. It is seen that these molecules behave like planar absorbers having a ratio of about 100 : 7 between the extinction coefficients along the long axis and perpendicular to it. Using this result and the experimental observations on absorption and dichroism in the retina in situ, a model for the configuration of chromophores in the disc membranes has been derived. In this model the plane of the chromophore is perpendicular to that of the disc and the long axis of the chromophore makes an angle of 6.6 degrees with the plane of the disc. The solution of the problem depends on the assumption that the absorption axes are the same for the rhodopsin, prelumirhodopsin and isorhodopsin.

Animals↗
PubMed1978

Flash photolysis of rhodopsin in rabbit.

Flash photolysis of rhodopsin in rabbit's retina has been analysed theoretically, and the results are found to be in good agreement with the experimental results of Hagins (1957). We have also obtained the variation of relative concentrations of rhodopsin, lumirhodopsin, isorhodopsin and metarhodopsin I during the period of the flash corresponding to two different intensities of the flash. It has been found that the quantum efficiencies of conversion of lumirhodopsin into rhodopsin and isorhodopsin will lie in the range 0.24--0.45 and 0.20--0.44 respectively; quantum efficiency of conversion of metarhodopsin I into rhodopsin and isorhodopsin are found to have values greater than 0.52 and 0.45 respectively and the quantum efficiency of conversion of isorhodopsin into lumirhodopsin has been found to be approximately 0.865. Also the maximum value of the rate constant of the reaction metarhodopsin I leads to metarhodopsin II at 37 degrees C has been determined in decerebrated eye and it has been found that it is of the same order as found by Pugh (1975) in the case of human eye.

Animals↗