Kinetic models of cell shape changes and other optically-detected responses to stimulation.

Certain cellular responses to stimulation can be described as a continuous series of virtually infinite but real transient states generated by reactions occurring at the molecular level within the cell. While any particular state can in principle be isolated and examined by using appropriate methods to stop or freeze the reaction, adjacent or nearby states will generally be indistinguishable from one another by kinetic means. In favorable cases, however, the progress curves can be fitted to comparatively very simple kinetic models involving a limited number of steps, which accurately describe the real-time response within the limitations of the experimental setup. The simple series models have their origins in the continuous myriad-state or "microscopic" series description, and the observable or "macroscopic" kinetic rate constants are statistically related to the rate constants describing the transitions between the real states of the ongoing response. This indicates that different aspects of stimulus-response coupling, e.g., shape changes, alterations in cytosolic calcium levels and so forth, can be compared in a self-consistent fashion by modeling the individual responses in terms of simple parallel series models.