Anion channel activity in the Chara plasma membrane: co-operative subunit phenomena and a model

Anion channel activity in the plasma membrane of internodal cells of Chara australis has been studied using the patch clamp method and the records analysed with a program based on the Hidden Markov Model. The activity was variable in time, and often showed very noisy periods. At other times there were one or more of five types of channel-like activity. These are believed, like the noise, to arise from the same anion-conducting mechanism in the membrane. The channel-like activity shows many current levels, the actual levels varying on a time-scale of the order of seconds. The records show non-independent transitions between levels, and thus the activity is not the result of the patch containing many independent channels. The currents often move sequentially between adjacent levels. The current levels are at times more closely spaced as the magnitude of the current increases. Underlying this sequential transition scheme it is found that current and conductance frequently show levels that are integer multiples of a unit. Typically about 10 levels occur, a typical transition scheme being (in units) 0↔4↔7↔9. It is shown that it is possible to model such sequential transition schemes with underlying units by considering a new model based on a random walk on a semiregular fragmentary tessellation of a plane.