Changes in cytoplasmic pH measured by ³¹P-NMR in cells of nitellopsis obtusa

The cytoplasmic pH of Nitellopsis obtusa measured by the ³¹P-nuclear magnetic resonance method was about 7.3. Since normal cell have a large vacuole, a long period of time is needed to accumulate signals for cytoplasmic phosphate. To measure the cytoplasmic pH in a shorter period, cytoplasm-rich cells were prepared by centrifugation. The cytoplasmic pH of these cells was also about 7.3. Illumination reversibly increased the cytoplasmic pH from 7.3 to 7.8. When the cytoplasm-rich cell was illuminated, the membrane potential hyperpolarized concomitant with the alkalification of the cytoplasm.