The phototransduction machinery in the rod outer segment has a strong efficacy gradient.
Rod photoreceptors consist of an outer segment (OS) and an inner segment. Inside the OS a biochemical machinery transforms the rhodopsin photoisomerization into electrical signal. This machinery has been treated as and is thought to be homogenous with marginal inhomogeneities. To verify this assumption, we developed a methodology based on special tapered optical fibers (TOFs) to deliver highly localized light stimulations. By using these TOFs, specific regions of the rod OS could be stimulated with spots of light highly confined in space. As the TOF is moved from the OS base toward its tip, the amplitude of saturating and single photon responses decreases, demonstrating that the efficacy of the transduction machinery is not uniform and is 5-10 times higher at the base than at the tip. This gradient of efficacy of the transduction machinery is attributed to a progressive depletion of the phosphodiesterase along the rod OS. Moreover we demonstrate that, using restricted spots of light, the duration of the photoresponse along the OS does not increase linearly with the light intensity as with diffuse light.
International School for Advanced Studies, 34136 Trieste, Italy; Cluster in Biomedicine S.c.r.l., 34149 Trieste, Italy;
Monica
M
Mazzolini
International School for Advanced Studies, 34136 Trieste, Italy;
Giuseppe
G
Facchetti
Cluster in Biomedicine S.c.r.l., 34149 Trieste, Italy;
Laura
L
Andolfi
Istituto Italiano di Tecnologia, 16163 Genova, Italy;
Remo
R
Proietti Zaccaria
Istituto Italiano di Tecnologia, 16163 Genova, Italy;
Salvatore
S
Tuccio
Rapp OptoElectronic, 22880 Wedel, Germany;
Johannes
J
Treu
International School for Advanced Studies, 34136 Trieste, Italy;
Claudio
C
Altafini
King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia; Bio-Nanotechnology and Engineering for Medicine, Department of Experimental and Clinical Medicine, University of Magna Graecia, 88100 Catanzaro, Italy; and.
Enzo M
EM
Di Fabrizio
Cluster in Biomedicine S.c.r.l., 34149 Trieste, Italy; Istituto Officina dei Materiali - Consiglio Nazionale delle Ricerche, 34149 Trieste, Italy.
Marco
M
Lazzarino
Rapp OptoElectronic, 22880 Wedel, Germany;
Gert
G
Rapp
International School for Advanced Studies, 34136 Trieste, Italy; torre@sissa.it.
Vincent
V
Torre
D000818:Animals; D003198:Computer Simulation; D007834:Lasers; D008297:Male; D008959:Models, Neurological; D018408:Patch-Clamp Techniques; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010775:Photic Stimulation; D012374:Rod Cell Outer Segment / Q000201:enzymology / Q000502:physiology*; D014785:Vision, Ocular / Q000502:physiology*; D014982:Xenopus laevis
D010727:Phosphoric Diester Hydrolases
cGMP diffusion; optical fiber; phosphodiesterase; phototransduction; rhodopsin