All living cells are bathed in extracellular fluid that differs in composition from the intracellular milieu. Activation of cells is characterized by alterations in cell membrane permeability and the resultant transmembrane movement of ions. The crucial membrane components are the various “channels” or “gates” that define the permeability or conductances of various ions. Sodium, potassium, magnesium, and calcium all play significant roles in biological activity, but calcium, because of its unique chemical properties, is the most crucial in terms of possessing a wide diversity of functions. The importance of this cation is underscored by the fact that no electrolyte is under more vigorous control in the body than calcium.
KeywordsCalcium Entry Acrosome Reaction General Introduction Cellular Calcium Adrenal Chromaffin Cell
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