AN ELECTROPHYSIOLOGICAL STUDY OF DROSOPHILA MUTANTS AFFECTING RHODOPSIN
Abstract
Mutations that decrease the amount of rhodopsin in the membrane of the photoreceptor in Drosophila melanogaster have previously been shown to have a reduced or absent prolonged depolarizing afterpotential and a decreased sensitivity to light stimuli. In the present study, an electrophysiological analysis of was carried out on several mutants of the nina class, that have substantial reductions in the rhodopsin content. The ninaE gene is probably the structural gene for the rhodopsin apoprotein, opsin. The ninaD gene product is likely involved in vitamin A metabolism, and a mutation in it can result in a reduced rhodopsin content. A detailed comparison of the light responses of a ninaE mutant, ninaE('P332), with a ninaD mutant, ninaD('P246), show the two have similar sensitivities. No significant differences that could be attributed specifically to a mutation in the opsin gene were found. In addition, this study has shown effects of reduced rhodopsin content on the physiology and structure of a photoreceptor. Greatly reducing the amount of rhodopsin in the rhabdomeric membrane results in a decrease in the membrane capacitance and increase in the membrane resistance. Both of the changes are likely to be due to a decrease in rhabdomeric surface area shown by Leonard and Pak (1984). Decreasing the rhodopsin level by 2 log units or more results in light induced bumps that are larger and have a different shape from wild type bumps at similar depolarization levels. Lowering the intracellular calcium concentration mimics the increased amplitude and changes the shape of the bumps, but also affects the latency and kinetics of the light response. It is suggested that greatly decreasing the amount of rhodopsin in the photoreceptor membrane results in allowing a greater number of intermediate enzymes to interact with rhodopsin, and thus a larger signal is sent to depolarize the membrane. In addition, this rhodopsin-enzyme interaction may be related to one of the sites of calcium action.
Degree
Ph.D.
Subject Area
Anatomy & physiology|Animals
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