Cellular Signaling Systems

This chapter explains mechanisms for the rise of cellular Ca²⁺ in two distinct cell types: nonexcitable and excitable cells. It discusses how metabolism is affected by a rise in intracellular Ca²⁺ concentrations. First, the elevation of Ca ²⁺ concentration in cells that leads to its signaling is considered here to arise exclusively from the internal pool of the endoplasmic reticular (ER) lumen. Excitation-contraction coupling is the process in which an electrical excitation of the plasma membrane causes a Ca ²⁺ release from internal stores of the cell. While skeletal muscle Ca ²⁺ signaling historically predates those of nonexcitable tissue, the pathway for Ca ²⁺ signaling is less fully understood in skeletal muscle, and even less clear in other excitable cells such as heart and neural cells. Considering a few targets in the liver illustrates how this signaling system can provide a change in metabolic climate.