Rate constants of the reactions for the first model.

Apart from k5 and k-5, all values were chosen according to [46]. Thus, k1, k-1, k2, k-2 were estimates from moth olfactory transduction or vertebrate phototransduction (see [46] for further references). For the parameters k5 and k-5 (see also Eqs. 13 and 14), the listed base-line values were chosen to mimic the experimentally measured dynamics of adenylate cyclase activation/deactivation in response to transmitter [42], for a detailed sensitivity-analysis, see Fig. 5A. k5 and k-5 were sensitive to Ca++ (Eqs. 13 and 14).