Subject(s)
Glucose/metabolism , Intestines/physiology , Sodium/pharmacology , 3-O-Methylglucose , Animals , Biological Transport, Active/drug effects , Electric Conductivity , Electrophysiology , Epithelium/physiology , Fructose/pharmacology , Glucose/pharmacology , Goldfish , Membrane Potentials/drug effects , Methylglucosides/pharmacology , Models, Biological , Ouabain/pharmacologyABSTRACT
The effects of mucosal application of monosaccharides and amino acids on transepithelial and membrane potentials in isolated goldfish intestinal epithelium were investigated. Isosmotic replacement of mucosal mannitol by sugars or L-amino acids resulted in a rapid depolarization of the mucosal membrane potential psi mc followed by a slow repolarization. Phlorizin inhibited the responses to sugar but not those to amino acids. D-Amino acids did not induce any electrical response in the epithelium. Dose-response curves for L-amino acids showed simple saturation. Simultaneous application of L-amino acid and glucose induced transepithelial responses of about 80% of the sum of the separate responses to the application of amino acid or glucose alone. Simultaneous application of different amino acids in saturating concentrations did not increase the magnitude of the electrical responses. From the measured changes in potentials we calculated the change in electromotive force across the mucosal (delta Em) and serosal (delta Es) membrane. The change in Em induced by combined application of alanine and glucose was 90% of the sum of the calculated values induced by glucose and alanine alone. The response of Es to both substrates was accelerated with respect to that of separate substrates alone. We conclude that by application of glucose in addition to alanine the influx of sodium is increased, thereby stimulating the basolaterally located electrogenic Na+/K+-pump. There are no indications for direct interaction of sugars and amino acids at the mucosal membrane of the intestinal epithelial cell.
Subject(s)
Amino Acids/pharmacology , Carbohydrates/pharmacology , Intestines/physiology , Sodium/pharmacology , 3-O-Methylglucose , Alanine/pharmacology , Animals , Biological Transport, Active/drug effects , Electrophysiology , Epithelium/physiology , Glucose/pharmacology , Goldfish , Intestinal Mucosa/physiology , Membrane Potentials/drug effects , Methylglucosides/pharmacologyABSTRACT
A method is described for building a low-voltage-drift differential dc amplifier featuring automatic zero adjustment, a high input impedance, and a bandwidth of 10 kHz. This is achieved by an asymmetric two-step process between the input signal and ground. Bandwidth can be extended by the use of a second amplifier during the ground-sampling time. The amplifier can be made with standard electronic components. A major advantage of this method is that an existing amplifier can easily be converted into a low-voltage-drift amplifier by adding the essential elements of the described automatic zero-adjusting amplifier to its input stage. To illustrate the method a practical example is constructed featuring a drift of 0.2 microV/ degrees C.
Subject(s)
Amplifiers, Electronic , Electronics, Medical/instrumentation , Automation , Electric Conductivity , Electric Impedance , Electronic Data Processing , Electronics , Equipment Design , TemperatureABSTRACT
Electrotonic spread can be measured in the basal cells of the human epidermis. The communication between neighboring cells is high, whereas no leak to the intercellular spaces could be detected. The specific resistance of the membranes between the cells is about 10 Omegacm(2). This finding suggests that for those particles that are able to pass the cell membrane the intracellular path through the epidermis is at least as suitable as the path through the intercellular spaces.
