Figure 9.

Abrupt transitions of [Ca²⁺]_i in single cells. Data were obtained from the experiments shown in Fig. 7 A. (A) Superimposition of control responses from eight cells shows rapid transitions from a high Ca²⁺ to a low Ca²⁺ plateau. (B) An amplitude histogram from period after Ca²⁺ readdition in the experiment shown in A is bimodal, indicating that cells spend most of their time in one of two well-defined states. (C) 2 μM antimycin A1 increases the frequency of transitions from the high to low Ca²⁺ states. (D) Amplitude histogram from period after Ca²⁺ readdition in the experiment shown in C. The high Ca²⁺ peak is somewhat lower than in the control cells, probably due to the slow decline in the high Ca²⁺ plateau illustrated in C.