Introduction to the membrane electrophysiology of mononuclear phagocytes

Abstract

The most thoroughly studied electrical phenomenon of the cell membrane is the action potential of nerve and skeletal muscle cells. An action potential is a sudden regenerative change in electrical potential difference (membrane potential) across the cell membrane, resulting from a change in the selective conductivity of the membrane to cations (positively charged ions) such as Na⁺, K⁺ and Ca²⁺ (1). The action potential is the fundamental information carrying signal of the nervous system. In skeletal muscle cells, however, the action potential triggers a transient rise of the intracellular Ca²⁺ concentration, which leads to muscle contraction. In the past electrophysiology has dealt mainly with this area of physiology, but advances in techniques for measurements in single cells have shown that membrane potential changes and the transmembrane movement of ions are an important link between the extracellular and intracellular environments of most cells and play a regulatory role in a wide range of cellular functions. For example, the fertilization of sea urchin eggs has been shown to be initiated by an action potential causing a change in the intracellular composition of H⁺ ions, which in turn activates processes leading to cell division (2). Secretion of substances such as actylcholine from neuromuscular junctions (1) and saliva from salivary glands (3) has been shown to be caused by increases of intracellular Ca²⁺ associated with transmembrane currents. In β-pancreatic cells, a specific role for a Ca²⁺-dependent K⁺ membrane conductance in the release of insulin, has been found (4). It seems therefore, that cellular electrical processes form an ubiquitous physiological mechanism with which cells can perform their functions.