Enrico Nasi, Ph.D.

Research

Ion channels and phototransduction

Our research focuses on the mechanisms of gating and permeation of the ion channels that mediate the receptor potential in visual cells, and the regulation of the light-transduction cascade. Although our studies have been guided by questions that pertain to photoreceptor physiology, our interests lie more generally in the areas of ion channels and cell signaling. Several research lines actively pursued in our laboratory revolve around two basic themes:

(a) The biochemical transduction cascade that couples light absorption to ion channel gating with a sufficient gain to enable a cell to generate a sizable response after activation of a single receptor molecule.

(b) The mechanisms of light adaptation that allow a photoreceptor to optimize its responsiveness over a wide range of ambient illumination, by modulating both sensitivity and photoresponse kinetics.

Our current experimental approaches rely primarily on single-cell electrophysiology, fluorescence monitoring of cytosolic calcium, Western blot analysis and immunocytochemistry. In addition, molecular biology tools, including PCR, in-situ hybridization, and siRNA are being utilized to identify and localize elements of the signaling cascades, and to corroborate their role in the visual process.

FIGURE 1: Light-activated single-channel currents recorded from a cell-attached patch of photosensitive membrane in an isolated microvillar photoreceptor. In the dark, no activity is detectable, but photostimulation causes vigorous opening of ion channels.

FIGURE 2: The double retina is composed by two distinct classes of photoreceptors. The cells shown were isolated enzymatically. The light-transducing machinery is located in the microvilli-covered lobe of rhabdomeric cells, and in the modified cilia of ciliary cells, respectively. (s = soma, a = axon stump, r = rhabdomeric lobe, c = ciliary appendages)

FIGURE 3: Localization of PKCa in the light-sensitive membrane of microvillar photoreceptors. This protein is a key participant in the process of light adaptation and is activated by the light-induced increase in calcium and diacylglycerol, which cause its translocation from the cytosol to the cell membrane. Top, left: Enzymatically dissociated photoreceptor fixed immediately after a brief light stimulus (R = light-transducing lobe ('rhabdomere'), S = soma, sp = screening pigment, g = glial cell). Top right: Immunofluorescence using anti PKCa primary antibodies. The staining is confined to the rhabdomeric membrane (some autofluorescence from screening pigment is also visible). The spatial profile of fluorescence intensity measured along the indicated line is plotted in the bottom panel.

Selected Publications:

Knox, B.E., Barlow, R.B., Thompson, D.A., Swanson, R. and Nasi, E. (2000). Expression of phototransducton proteins in Xenopus oocytes. Methods in Enzymology, 316: pp.40-51.

Piccoli, G., Gomez, M. and Nasi, E. (2002). Role of protein kinase C in light adaptation of microvillar photoreceptors. Journal of Physiology. 543: 481-494.

Gomez, M. and Nasi, E. (2005). Calcium-independent, cGMP-mediated light adaptation in ciliary photoreceptors. Journal of Neuroscience. 25: 2042-2049.

Gomez, M. and Nasi, E. (2005). A direct signalling role for PIP2 in the visual excitation process of microvillar receptors. Journal of Biological Chemistry. 280:16784-16789.

Gomez, M. and Nasi, E. (2005). On the gating mechanism of cGMP-activated channels of hyperpolarizing photoreceptors: does light remove inactivation in voltage-dependent k channels? Journal of General Physiology.125: 455-464.

Gomez, M. and Nasi, E. A slow light-induced current in microvillar photoreceptors mediating store-operated calcium influx (Submitted for publication).

Complete list of Publications

Contact Us

Enrico Nasi, Ph.D.
Department of Physiology and Biophysics
Boston University School of Medicine
715 Albany Street
Boston MA 02118-2526

Phone:(617) 638-4347
Fax: (617) 638-4273
e-mail: enasi@bu.edu