The large cells enable biologists to use a variety of experimental methods to measure the movement of ions and molecules in and out of cells. A disease with dozens of faces The effort to piece together a picture of how retinas adapt to changing light and the abberations that cause abnormalities in the adaptive process has been complemented, in recent years, by a search for the genetic defects that cause retinitis pigmentosa. Scientists use a patch pipette and two puffer pipettes to dispense neuroactive agents into a skate retinal cell. It turns out that retinitis pigmentosa may be caused by many different genetic mutations, Ripps says. Already more than 75 mutations have been identified in genes that code for the protein rhodopsin, the molecule found in the retinal rods that actually detects light.
Some people have normal rhodopsin but nonetheless suffer night blindness and retinal degeneration.
This suggests that retinitis pigmentosa can also be caused by defects in other proteins in the rods or in retinal cells other than photoreceptors. Retinitis pigmentosa serves as a reminder that finding a disease gene is not synonymous with finding a cure. With the genes in hand, the challenge remains to figure out exactly how defective proteins cause disease. The other approach is to keep piecing together the picture of how vision works in a normal, healthy model system. The gathering appreciation of how retinas work is also laying the foundations for gene therapies or, possibly, for transplantation of rod and cone cells.