THE SATURATED RESPONSE OF VERTEBRATE RODS AND ITS RELATION TO CGMP METABOLISM

Strong light flashes saturate the response of a rod, and increasing fl ash intensities prolong the period of saturation. We have found that t he period of saturation lengthens from base to tip of the outer segmen t and we have shown that free cGMP is replenished locally to terminate saturation and not in the G-cyclase rich axonemal region near the inn er segment which contains the cell mitochondria. Our results also show that each section of outer segment acts as an independent module in t his phase of transduction.