![\"M.](\"http:\/\/www.bumc.bu.edu\/phys-biophys\/files\/images\/cornwall1.jpg\")
<\/p>\n<\/p>\n
Professor of Physiology and Biophysics<\/p>\n
B.S. University of Utah
\nPh.D. University of Utah<\/p>\n
Phone: (617) 638-4256 The work in our laboratory is focused on understanding the response Bleaching of rhodopsin (Rh) produces a photoactivated methrhodopsin Our most recent work has focused on the time course of changes in Cornwall, M.C. and G.L. Fain (1994) Bleached Cornwall, M.C., H.R. Matthews, R.K. Crouch and Matthews, H.R., G.L. Fain, and M.C. Cornwall. Matthews, H.R., M.C. Cornwall, and G.L. Fain. Matthews, H.R., G.L. Fain, and M.C. Cornwall Fain, G.L., H.R. Matthews, and M. C. Cornwall. (1996) Dark adaptation in vertebrate photoreceptors. TINS 19:502-507.<\/p>\n Sampath, A.P., H.R. Matthews, M. C. Cornwall, J. Kefalov, V.J., M. C. Cornwall, and R.K. Crouch Department of Physiology and Biophysics
\nFax: (617) 638-4273
\ne-mail: cornwall@bu.edu<\/a>
\naddress: see below<\/a><\/p>\n<\/a>Research<\/h2>\n
Dark Adaptation in Vertebrate Photoreceptors<\/h3>\n
\nof the vertebrate eye to and recovery from the effects of bright light.
\nOur principal approach is to make electrophysiological measurements of
\nrod and cone photoreceptors of cold-blooded vertebrate animals, and to
\ncorrelate these physiological responses to microspectrophotomeric
\nmeasurements of the visual pigments as well as microfluorometric
\nmeasurements of the concentration of vitamin A and Ca2+ contained within
\nthe cells. The reduction of all\u2013trans retinal to Vitamin A is one of
\nthe principal initial steps that must occur following exposure to bright
\nlight to allow recovery of sensitivity (dark adaptation). Experiments
\nhave also shown that Ca2+ is a principal messenger substance during
\nbright (bleaching) adaptation.<\/p>\nThe Visual Cycle<\/h4>\n
![\"\"](\"http:\/\/www.bumc.bu.edu\/phys-biophys\/files\/images\/carter1.jpg\")
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\nII (R*), which decays through a series of intermediates to opsin and
\nall-trans retinal. All-trans retinal is reduced within the photoreceptor
\nto all-trans retinol, which is then transported via the
\ninterphotoreceptor retinol binding protein (IRBP) through the
\nextracellular space to an adjacent layer of epithelial cells, called the
\nretinal pigment epithelium (RPE). Within the RPE, the all-trans retinal
\nis bound to cellular retinol binding protein (not shown) and then is
\nesterified to fatty acits, mostly palmitic acid. The ester is converted
\nby retinoid isomerase to 11-cis retinol, which is bound to yet another
\nbinding protein and oxidized by oxidoreductase to 11-cis retinal.
\nInterphotoreceptor binding protein then returns the 11-cis retinal to
\nthe photreceptor, where it recombines with opsin to form dark adapted
\nRh.<\/p>\nRetinol Fluorescence<\/h4>\n
![\"\"](\"http:\/\/www.bumc.bu.edu\/phys-biophys\/files\/images\/carter31.jpg\")
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\nretinol fluorescence intensity following a large bleach of the visual
\npigment. The bright field image at top left shows cellular fragments as
\nwell as one intact cone (lower left) and one intact red rod (upper
\nright). The cells were suspended in a bath that had been mounted on the
\nstage of the fluorescence microscope. The second field on the top row
\nshows a fluorescence image obtained before visual pigment bleaching (T =
\n0.00 min). It is apparent that both intact cells exhibit a large amount
\nof fluorescence in their ellipsoid regions. This fluorescence is
\nconsistent with the large concentration of mitochondria located there,
\nand likely results from the high concentration of NADH in mitochondria.
\nThe cell was then exposed to sufficient bright green (500 nm) light to
\nbleach in excess of 99% of the visual pigment contained in the outer
\nsegments of both cells. The top right panel (T = 0.52 min.) shows a
\nlarge uniform increase in fluorescence in the region of the cone outer
\nsegment, and a small amount of fluorescence beginning to appear in the
\nmost proximal part of the outer segment of the rod. The bottom panel on
\nthe left (T = 13.09 min.) shows that by this time, much of the outer
\nsegment fluorescence in the cone had dissipated; however, the
\nfluorescence in the rod outer segment continued to increase, and
\nappeared to uniformly fill the outer segment of the rod. The image in
\nthe second panel from the left, bottom row (T = 37.80 min.) shows that
\nthe fluorescence in the cone outer segment by this time was very low,
\nbut that in the outer segment of the rod had achieved a maximum level.
\nAt this time 2 :m bovine IRBP was added to the bath. Thereafter, the
\nfluorescence in the rod outer segment was observed to decline. The last
\nmeasurement of fluorescence was made 87.82 min following the initial
\npigment bleach.<\/p>\n<\/a>Publications<\/strong><\/h2>\n
\npigment activates transduction in isolated rods of the salamander
\nretina. J. Physiol. 480: 261-279.<\/p>\n
\nG.L. Fain. (1995) Bleached pigment activates phototransduction in
\nsalamander cones. J. Gen. Physiol. 106: 543-557.<\/p>\n
\n(1995) Role of cytoplasmic calcium concentration in the bleaching
\nadaptation of salamander cone photoreceptors. J. Physiol. 490: 293-303.<\/p>\n
\n(1996) Persistent activation of transducin by bleached rhodopsin in
\nretinal rods. J. Gen Physiol. 108:557-563.<\/p>\n
\n(1996) Role of cytoplasmic calcium concentration in the bleaching
\nadaptation of salamander cone photoreceptors. J. Physiol. 490:293-303.<\/p>\n
\nBandarchi, and G.L. Fain. (1999) Light-dependent changes in outer
\nsegment free-Ca2+ concentration in salamander cone photoreceptors. J.
\nGen Physiol. 113:1-11.<\/p>\n
\n(1999) Occupancy of the chromophore binding site of opsin activates
\nvisual transduction in rod photoreceptors. J. Gen. Physiol. 113:491-503.<\/p>\n<\/a>Contact Us<\/h2>\n
\nBoston University Chobanian & Avedisian School of Medicine
\n72 East Concord Street
\nBoston MA 02118-2526<\/p>\n