Fig. 2.
Model of QB generation. (a) An example of temporal evolution of the key dynamical variables during a QB. The input module produces ≈5 PLC*, with significant fluctuations. The number of A* molecules rises slowly until it reaches the level AT, when channels start opening rapidly (sharp increase of B*). The value of AT is larger than AQB, the threshold for generating reliable QB. The observed variability in latency, see b, is largely attributable to the fluctuations of the levels AT at which the QB starts. Ultimately, the Ca-dependent inhibitor C* gets produced and terminates the QB. (b) Simulated QBs elicited by activation of a single M* at t = 0. A brief (≈20 ms) opening of ≈20 channels occurs after a latency of ≈80 ms. A significant variability can be seen from the traces, in particular in the latency time, whose distribution is shown at the top. (c) The domain of QB generation in the PLC*–[Ca2+]ex plane defined by the condition that opening of a single channel will, with high probability, generate the opening of many more channels. The star denotes the operating point corresponding to the WT.