ABSTRACT
This chapter discusses experimental and theoretical considerations related to intracellular gradients of calcium and hydrogen ions. The diffusion of calcium ions in cytoplasm cannot be expected to resemble that in free solution. In cytoplasm, a host of Ca-binding and sequestering entities are present, complicating the diffusion process. Calcium gradients from the surface membrane into the axoplasm have been deduced from experiments in which aequorin was injected into the squid giant axon. This protein, extracted from the jelly fish emits light in the presence of calcium. In many types of cells, a rapid transient rise in intracellular calcium has been shown to be a necessary link between an extracellular signal or an electrical event in the surface membrane and some functional activity of the cell. The cell may be considered as a surface membrane dividing an extracellular medium from an intracellular compartment of uniform composition.
