Light-Induced Membrane Hyperpolarization and Adenine Nucleotide Levels in Perfused Characean Cells

This study examines the relationship between light-induced membranehyperpolarization and changes in adenine nucleotide levels intonoplast-free characean cells. When cells were perfused witha medium containing 1 mM ATP in the dark, the plasma membranedepolarized, the cytosolic ATP level decreased, and the ADPand AMP levels increased. Under light, the membrane hyperpolarized,the ATP level increased, and the ADP and AMP levels decreased.These changes in the adenine-nucleotide levels could partiallyexplain the membrane hyperpolarization. When cells were perfusedwith a medium containing an ATP-regenerating system consistingof phosphoenolpyruvate and pyruvate kinase, the membrane potentialremained in the hyperpolarized state, the ATP level remainedat a high level and no light-induced hyperpolarization was observed.The intracellular adenine nucleotide levels were also controlledby continuous perfusion. The membrane potential was determinedonly by the adenine nucleotide levels of perfusion media, irrespectiveof the light condition. Chloroplast-free Nitellopsis cells into which isolated Pisumchloroplasts were introduced also showed light-induced membranehyperpolarization. Pretreatment of chloroplasts with dicyclohexylcarbodiimide(DCCD) completely abolished the hyperpolarization with parallelinhibition of photophosphorylation. These results strongly suggestthat changes in adenine nucleotide levels caused by photophosphorylationare responsible for light-induced membrane hyperpolarizationin perfused cells. (Received August 17, 1985; Accepted December 13, 1985)