On the metabolism of the rod outer segments.

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Abstract
The high energy phosphate esters [HEPE] available for the luminescent reaction of the firefly lantern extract corresponded in the dark-adapted rods of the frog [Rana catesbeiana] to 7 .times. 10-16 mol of ATP/rod, corresponding to about 1.4 mM. Rods isolated from light-adapted eyes contained a smaller amount. The HEPE were reduced spontaneously at a rate of 50% in 24 min in the isolated rods in darkness. Bleaching a few per cent of the rhodopsin molecules of a rod suspension induced a 60% decrease achieved in less than 12 s. The ionophore A23187 decreased the HEPE when the extracellular free Ca2+ concentration was greater than 10-7 M, suggesting that ATP was consumed in pumping Ca2+ out of the rods, or into the disks contained in the rods, or both.