Membrane potential can be determined in individual cells from the nernstian distribution of cationic dyes.

Calcium in biological systems

Lymphocyte membrane potential assessed with fluorescent probes

Publisher Summary Gap junction channels are often regarded by membranologists as an unusual means of membrane permeability, having little in common with other membranous channels. Although gap junction channels establish hydrophilic paths between two cells' interiors and are a permissive type of channel, as they are bidirectionally and indiscriminately permeable to charged and neutral molecules, they have many structural and functional similarities with other membranous channels. Not only can they be easily localized in intact cells and studied by ultrastructural methods, such as thin sections, lanthanum infiltration, freeze-fracture, and negative staining, they can also be isolated in quite pure fractions and characterized chemically. Because of their crystalline configuration in isolated fractions, they can be studied by laser, X-ray, and electron diffraction techniques. Their permeability properties and the mechanisms of permeability modulation can be studied electrophysiologically, morphologically, and by tracer-transfer methods. Thus, in the years to come, gap junction channels will be recognized as one of the most useful and exciting model systems to be exploited in studying the general properties of membranous channels.

Structural correlates of gap junction permeation.

The fertilization potential, or activation potential, has been demonstrated in the eggs of various species, and it has been shown to block polyspermy in echinoderm, echiuran and frog eggs, but no studies have been reported of electrical phenomena occurring when mammalian eggs are fertilized. We report here the fertilization potential of golden hamster eggs in vitro. To correlate the change of potential with the interaction between sperm and egg, only one sperm was attached to each egg. We found that a sperm induces recurring hyperpolarizations, constituting a fertilization potential which differs from that in the eggs of other species.

Fertilization potential in golden hamster eggs consists of recurring hyperpolarizations.

Summary Microelectrode studies of human lymphocytes after 24 to 48 hr of stimulation by phytohemagglutinin are described. A stable transmembrane potential of about -18 mV was detected. The input resistance of these cells was about 5 megohms. Clumps of stimulated cells exhibit junctional communication as revealed by coupling coefficients of 0.2 to 0.6. No changes in membrane properties and intercellular communication were detected throughout the observed period. The results reported here suggest that the establishment of interlymphocyte communication is possibly involved in the control of mitosis.

Intercellular communication in stimulated human lymphocytes.

Electrophysiology of phagocytic membranes. I. Potassium-dependent slow membrane hyperpolarizations in mice macrophages

Electrophysiology of phagocytic membranes. II. Membrane potential and induction of slow hyperpolarizations in activated macrophages.

Some electrophysiological characteristics of macrophages and macrophage polykaryons of foreign body granuloma have been investigated. Cells were obtained from implants of small coverslips in the subcutaneous tissue or in the peritoneal cavity of rats and mice. Transmembrane potentials ranged from −5 to −40 mV. Input resistances ranged from 5 to 120 MΩ, being significantly higher in mice polykaryons. Approximately 10% of the cells exhibited spontaneous slow membrane hyperpolarizations (SH) indistinguishable from those observed in macrophages. SH responses were invariably evoked by iontophoretic injection of calcium ions into the cytoplasm of mice macrophages or macrophage polykaryons. The amplitude of these responses increased with the amount of current carried by calcium ions into the cells. The maximum amplitude of the calcium-induced SH responses is a linear function of the logarithm of [K+]
 0
 (from 3 to 40mm). The slope of the regression line is 43 mV for a 10-fold increase in [K+]
 0
 . Substituting sodium chloride by sodium isethionate or by choline chloride does not interfere with the occurrence of SH. The assumption that the SH is solely a consequence of an increase in the membrane conductance to K+ was used to calculate the potassium equilibrium potential (E
K). TheE
K value is also a linear function of the logarithm of [K+]
 0
 (from 3 to 40mm). The slope of the regression line is 46 mV for a 10-fold increase in [K+]
 0
 . These results constitute evidence of the calcium dependence of K+ permeability during SH both in macrophages and macrophage polykaryons. Macrophage polykaryons are a more convenient model than macrophages for the study of the mechanisms underlying the SH responses and their possible physiological implications.

Electrophysiology of phagocytic membranes: induction of slow membrane hyperpolarizations in macrophages and macrophage polykaryons by intracellular calcium injection.

Electrophysiology of phagocytic membranes. III. Evidence for a calcium-dependent potassium permeability change during slow hyperpolarizations of activated macrophages.

Gilberto M. Oliveira-Castro

Papers

Intercellular communication in stimulated human lymphocytes.

Electrophysiology of phagocytic membranes. I. Potassium-dependent slow membrane hyperpolarizations in mice macrophages

Electrophysiology of phagocytic membranes. II. Membrane potential and induction of slow hyperpolarizations in activated macrophages.

Electrophysiology of phagocytic membranes: induction of slow membrane hyperpolarizations in macrophages and macrophage polykaryons by intracellular calcium injection.

Electrophysiology of phagocytic membranes. III. Evidence for a calcium-dependent potassium permeability change during slow hyperpolarizations of activated macrophages.