ABSTRACT
Calcium ions play a critical role in numerous essential bio logic processes, and the importance of calcium as a mes senger system cannot be overstated (1). Calcium has a central role in mediating the contraction of all forms of muscle, the secretion of exocrine, endocrine, and neuro endocrine products, the metabolic processes of glycogenolysis and gluconeogenesis, the transport and secretion of fluids and electrolytes, and the growth of cells (2,3). In particular, calcium catalyzes enzymatic reactions that split high-energy phosphate bonds and are involved in the elec trical activation of excitable cells, hemostasis, and metab olism of bone (Table 22-1) (4). In terms of clinical effects that relate to calcium channel blockers, calcium ion influx is primarily involved in the genesis of the cardiac action potential (2), facilitates the intracardiac conduction of electrical impulses (5), promotes contraction of cardiac and smooth muscle cells, and may also cause irreversible cellular injury of anoxic tissue (2,4).
