Analysis of rapid light-induced potential change in cells of chara corallina

Perfused Chara cells were used to measure the rapid light-induced potential change (rapid LPC) caused by activation of a K⁺ channel in the plasma membrane through photosynthesis in the presence of various photosynthetic inhibitors. The rapid LPC was inhibited by DCMU but recovered on addition of phenazinemethosulfate (PMS) in the presence of DCMU. Carbonylcyanide m-chlorophenylhydrazone (CCCP) stimulated the rapid LPC. DCCD partially inhibited the rapid LPC with a partial inhibition of oxygen evolution. It is concluded that both cyclic and noncyclic electron flows are coupled with the rapid LPC.To understand the mechanism of K⁺ channel activation by photosynthetic electron flow, the rapid LPC was measured under continuous internal perfusion. It was suggested that a diffusible substance was not released from chloroplasts, since vigorous continuous perfusion did not inhibit the rapid LPC.The suggestion that the rapid LPC is caused by changes in surface charge density of chloroplasts was supported by the fact that the rapid LPC was inhibited by increasing the ionic strength of the perfusion medium.