Thursday, January 22, 2004

Skewering Fly Eyes in the Dark, What Fun!

Some of you may be wondering what it is I've been doing locked away in a dark room all week. I've been imaging fruit fly eye cells (also called photoreceptors) that contain fluorescent proteins and recording the electrical current that passes through them. I do this by literally poking the cells with a microscopic electrode and taking pictures with a CCD camera attached to a microscope. First I have to cut off several flies heads, rip the eyes off with tweezers, and then dissociate the eye cells by pulling them up and down in a pipette tip. After squirting the cells in a recording dish under the microscope, I carefully place a glass electrode right on a cell and gently use suction and a electrical pulse to rupture a hole in the cell membrane. The cells are about 15-20 micrometers (or microns) in length and the tip of the electrode is about 1-2 microns in diameter (see below).

What you see in the picture is an individual unit eye or ommatidium that is a cluster of 8 photoreceptors. The electrode is stuck to one of the cells in the cluster. I can measure the electrical current passing into the cell when light activates sodium channels in the cell membrane. The normal state of the inside of the cell is slightly negative, about -70 millivolts (mV). When the sodium channels open, positive sodium charges rush in and cause the inside of the cell to become more positive. The signal I read out on the oscilloscope looks similar to the one below. The blue arrow indicates where the light flash went off. The y axis is in picoamps (pA) and the x axis is in milliseconds (ms).

I wrote a post earlier on calcium imaging with a picture of a fluorescent photoreceptor here and here.
And there you have it. A genuine electrical recording from a tiny little fly photoreceptor cell. If you are a science geek and want more information on electrophysiology recordings of cell see this link.

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