Studies of the blood chemistry of Electrophorus electricus and a new physiological saline solution based thereon

Based upon analyses of the composition of electric eel blood serum we suggest a new physiological saline solution as follows: 188 mM NaCl, 5 mM KCl, 2 mM MgCl₂, 2 mM CaCl₂, 0.15 mM NaH₂PO₄, 1.45 mM Na₂HPO₄ and 5 mM glucose; pH 7.4. The major difference between this saline and that used in most of the previous investigations using eel electroplaques is that the total Na⁺ concentration is increased from between 162.7 and 171.7 mequiv/l to 191 mequiv./l. This increase does not appear to affect the electrophysiological properties of the electroplaque.     

Morphological study of the heart of Electrophorus electricus

Hearts of 7 Electrophorus electricus have been investigated on macroscopical and microscopical levels. Generally, the structure of the heart exhibits relative similarities with the other studied teleosts. The ventricular myocardium is mainly spongy and suggests that these structural features can offer an additional contraction power.     

Half-of-the-sites reactivity of the membrane-bound Electrophorus electricus acetylcholine receptor

Equilibrium binding studies of the interaction of activators (decamethonium, carbamylcholine) and inhibitors (d-tubocurarine, α-bungarotoxin) of membrane electrical potential changes in electroplax membrane preparations from $\text{Electrophorus electricus}$ have been carried out at 4°C, in cel Ringer solution, pH 7.0. The properties of the interaction of these chemical mediators with the membrane-bound receptor appear to be similar to those observed with regulatory enzymes which exhibit an allosteric mechanism involving ligand-induced conformational changes. The data presented here show that activators and inhibitors compete for only one-half the available membrane sites. The experiments also provide additional support for the interpretation of kinetic studies which indicated that electroplax membranes contain two different binding sites, one for activators and one for inhibitors of electrical membrane potential changes.     

The morphological study of the respiratory organ of Electrophorus electricus

The respiratory organ of Electrophorus electricus is located in the oral cavity and is formed by papillar structures. The papilla consists basically of a cartilaginous central nucleus and is bounded by a connective layer. The results reveal structural adaptations for the respiration among fishes which have efficient respiratory circulation related with the venous blood.     

Electrophorus electricus as a model system for the study of membrane excitability

The stunning sensations produced by electric fish, particularly the electric eel, Electrophorus electricus, have fascinated scientists for centuries. Within the last 50 years, however, electric cells of Electrophorus have provided a unique model system that is both specialized and appropriate for the study of excitable cell membrane electrophysiology and biochemistry. Electric tissue generates whole animal electrical discharges by means of membrane potentials that are remarkably similar to those of mammalian neurons, myocytes and secretory cells. Electrocytes express ion channels, ATPases and signal transduction proteins common to these other excitable cells. Action potentials of electrocytes represent the specialized end function of electric tissue whereas other excitable cells use membrane potential changes to trigger sophisticated cellular processes, such as myofilament cross-bridging for contraction, or exocytosis for secretion. Because electric tissue lacks these functions and the proteins associated with them, it provides a highly specialized membrane model system. This review examines the basic mechanisms involved in the generation of the electrical discharge of the electric eel and the membrane proteins involved. The valuable contributions that electric tissue continues to make toward the understanding of excitable cell physiology and biochemistry are summarized, particularly those studies using electrocytes as a model system for the study of the regulation of membrane excitability by second messengers and signal transduction pathways.     

Interaction and inhibition of acetylcholinesterase from Electrophorus electricus by nitrosamines

Kinetic analysis has shown that dimethylnitrosamine, dipropylnitrosamine, dibutylnitrosamine, and diphenylnitrosamine initially act as reversible competitive inhibitors with respect to the substrate, acetylthiocholine chloride. The inhibitor constants Ki vary from 21-30 microM for the aliphatic nitrosamines to 8.2 microM for the aromatic diphenylnitrosamine. With time they act as irreversible covalent inhibitors with dimethylnitrosamine producing 82% inactivation after 40 min. Pseudo-first-order kinetics are observed with the rate constant being proportional to the concentration of the nitrosamine and the order of reaction being equal to one. Fluorometry, gel chromatography, and equilibrium dialysis have been used to study the binding of the nitrosamines with acetylcholinesterase. Scatchard analysis indicates that dimethyl-, dipropyl-, and dibutylnitrosamine have a weaker affinity for the enzyme (Kd 5.6-8.08 microM) compared to diphenylnitrosamine (Kd 2.32 microM). In all cases the number of binding sites was four.     

Identification of a 55-kDa high-affinity calmodulin-binding protein from Electrophorus electricus

A high-affinity calcium-dependent calmodulin-binding protein (CaMBP) has been isolated from Electrophorus electricus main electric organ. This 55-kDa CaMBP has been purified to homogeneity by ion exchange and calmodulin-Sepharose affinity chromatography and electrophoretic elution from preparative sodium dodecyl sulfate-polyacrylamide gels. Antibodies against the 55-kDa CaMBP were raised in sheep and were affinity purified. A 47-kDa high-affinity CaMBP species was demonstrated by limited protease digestion and immunoblot analysis to be derived from the 55-kDa CaMBP. The 55-kDa CaMBP has also been isolated from skeletal muscle. It is not detectable by immunoblot analysis in nonexcitable tissues. Characterization of the 55-kDa high-affinity calmodulin-acceptor protein may further elucidate the role of calcium-calmodulin in the regulation of bioelectricity.     

Biochemical characterization of the tetrodotoxin binding protein from Electrophorus electricus

Biochemical properties of a detergent-solubilized tetrodotoxin binding component from Electrophorus electricus have been examined and compared with those found for the membrane-bound protein. The toxin binding component was solubilized with high efficiency by a variety of nonionic detergents and with lower efficiency by sodium cholate and deoxycholate. Detergent-solubilized preparations bound tetrodotoxin and saxitoxin tightly and specifically, and this binding was observed to be rapidly and irreversibly blocked by carboxylate-modifying reagents. Inactivation by carbodiimide and glycine ester or by a trimethyloxonium salt could be prevented by tetrodotoxin occupancy of the binding site. Tetrodotoxin binding activity in both solubilized preparations and in membranes was found to be highly resistant to proteases. In contrast, the activity was extremely sensitive to the action of phospholipase A2. The biochemical properties of the tetrodotoxin binding component solubilized in mixed lipid-detergent micelles are similar to those found in native membranes, with respect to the characteristics of equilibrium toxin binding and to the sensitivity of toxin binding activity to chemical modification and degradative enzymes. There were some differences with respect to the kinetics of tetrodotoxin binding. In addition, the tetrodotoxin binding component from eel is shown to behave as a glycoprotein, being selectively absorbed to resins coupled to concanavalin A, wheat germ agglutinin, Lens culinaris lectin, and ricin with the appropriate glycoside.     

Purification of acetylcholine receptors from the muscle of Electrophorus electricus

Muscle from the electric eel Electrophorus electricus contains acetylcholine receptors at 50 times the concentration of normal mammalian muscle and fully one-tenth the concentration of receptors in its electric organ tissue. Receptor is organized much more diffusely over the surface of Electrophorus muscle cells than is the case in normally innervated mammalian skeletal muscle. Receptor was purified from Electrophorus muscle by affinity chromatography on cobra toxin-agarose and found to contain subunits which correspond immunochemically to the alpha, beta, gamma, and delta subunits of receptor from electric organ tissue of Torpedo californica. Receptor purified from Electrophorus muscle appears virtually identical with receptor purified from Electrophorus electric organ tissue.     

Localization of actin in the electrocyte of Electrophorus electricus L.

Summary The cytoplasm of the electrocyte of Electrophorus electricus possesses a meshwork of 7-nm thick filaments distributed throughout the cell. Observation of stereopairs of transmission electron micrographs shows association of the filaments with the plasma membrane and the membranes of cytoplasmic organelles. Intense fluorescence, indicative of the presence of actin, was observed in the cytoplasm of electrocytes incubated in the presence of NBD-phallacidin or anti-actin antibodies.     

Alpha-actinin in the electric organ of Electrophorus electricus, L

We have identified Alpha-actinin from the electric organ of the Electrophorus electricus, L. It was analysed by polyacrylamide gel electrophoresis, and identified by immunoblotting. This protein was also found in a membrane fraction of the electric organ enriched with components of the cytoskeleton. Our results suggest that this protein might play a role either in the organization of the microfilaments or its interactions with the membrane to maintain a polarized electrocyte.     

Desmin heterogeneity in the main electric organ of Electrophorus electricus

Desmin, the muscle-specific intermediate filament protein was purified from the main electric organ of Electrophorus electricus. It is shown that pure desmin can be separated into 5 isoforms presenting different isoelectric points. These isoforms have similar molecular weight, react with an antibody directed against desmin and generate identical peptides after digestion with protease V8 from Staphylococcus aureus.     

Characterization of desmin in the electric organ of Electrophorus electricus L

The intermediate filament protein of the electric organ from the Electrophorus electricus L. was purified in DEAE-cellulose column after extraction with a Triton X-100 buffer and urea solubilization. The desmin was analysed by SDS-PAGE against desmin purified from chicken gizzard. Characterization of desmin from the electric eel was carried out by peptide mapping and immunoblotting methods.     

Scanning electron microscopy of the electric organs of Electrophorus electricus L

Summary The surfaces of the organs of Sachs and Hunter of Electrophorus electricus L. were examined by scanning electron microscopy. Special attention was directed to morphological details of the electrocyte to provide a better understanding of its anterior and posterior faces. Some aspects of the microanatomy of these organs, which differ markedly from those of the main electric organ, provide new information on the structure as revealed previously by light and transmission electron microscopy. The relief, mainly expressed by papillae, is related to the actual membrane area, which is important for calculations of specific resistance and conductance. Information is also presented on the general organization of the tissue, in particular the distribution of the connective elements and external configuration of synaptic terminals. Shrinkage in preparation of tissue was evaluated and correction made whenever necessary. Correction factors for actual membrane area were calculated for anterior and posterior faces of electrocytes from both organs.