Calcium dynamics: analyzing the Ca2+ regulatory network in intact cells

Calcium signaling is critical for all cells. As a free ion (Ca2+), calcium links many physiological stimuli to their intracellular effectors by interacting with binding proteins whose occupancy determines the cellular effect of stimulation. Because binding site occupancy depends on the history of Ca2+ concentration ([Ca2+]), Ca2+ dynamics are critical. Calcium dynamics depend on the functional interplay between Ca2+ transport and buffering systems whose activities depend nonlinearly on [Ca2+]. Thus, understanding Ca2+ dynamics requires detailed information about these Ca2+ handling systems and their regulation in intact cells. However, effective methods for measuring and characterizing intracellular Ca2+ handling have not been available until recently. Using concepts relating voltage-gated ion-channel activity to membrane potential dynamics, we developed such methods to analyze Ca2+ fluxes in intact cells. Here we describe this approach and applications to understanding depolarization-induced Ca2+ responses in sympathetic neurons.