Well-defined Conductance Research Articles

Corticosteroid modulation of hippocampal potentials: increased effect with aging.

Adrenal steroids bind specifically to hippocampal neurons under normal conditions and may contribute to hippocampal cell loss during aging, but little is known about the neurophysiological mechanisms by which they may change hippocampal cell functions. In the present studies, adrenal steroids have been shown to modulate a well-defined membrane conductance in hippocampal pyramidal cells. The calcium-dependent slow afterhyperpolarization is reduced in hippocampal slices from adrenalectomized rats, and it is increased after in vivo or in vitro administration of the adrenal steroid, corticosterone. Calcium action potentials are also reduced in adrenalectomized animals, indicating that the primary effect of corticosteroids may be on calcium conductance. The afterhyperpolarization component reduced by adrenalectomy is greater in aged rats than in young rats, suggesting that, with aging, there is an increased effect of corticosteroids on some calcium-mediated brain processes. Because elevated concentrations of intracellular calcium can be cytotoxic, these observations may increase the understanding of glucocorticoid involvement in brain aging as well as of the normal functions of these steroids in the brain.

Two purified fractions of alamethicin have different conductance properties

The properties of two purified alamethicin fractions, Fraction 4 and Fraction 6, have been studied in phosphatidylethanolamine (PE) membranes and phosphatidylserine (PS) membranes. Membranes doped with Fraction 4 show well-defined single channel conductance (mean lifetime about 20 ms). The autocorrelation function of the current fluctuations has one relaxation time of the same order as the mean lifetime of the single channels, and the current response to a voltage pulse follows an exponential with only one time constant. The conductance of a membrane doped with Fraction 6 has a voltage-independent part and a current-voltage curve with a slope that is half the slope of the Fraction 4 current-voltage curve. In the presence of Fraction 6, PS membranes and PE membranes both have symmetrical current-voltage curves even with Fraction 6 added to only one side. We did not detect any well-defined single channel levels in the presence of Fraction 6, and autocorrelation analysis of the current due to Fraction 6 gave two characteristic correlation times: a fast time (about 5 ms) and a slow time (about 50 ms). High current level kinetics of Fraction 6 also show two time constants. A possible explanation for the differences between the two fractions is that Fraction 6 monomers have a lower dipole moment than those of Fraction 4. The difference in channel stability can be explained by a lowered tendency of the monomers to line up parallel to the field. The negative branch and voltage-independent conductance can be explained by lowered energy of insertion of monomers into the membrane, and lowered energy of interaction between the monomers and the electric field.

2-methoxyethanol as a solvent for conductometric acid-base titrations

Conductometric titrations of a series of organic acids in 2-methoxyethanol were performed with 1,3-diphenylguanidine (DPG) as titrant. For benzoic, p-chlorobenzoic and picric acids, phenylphenol and barbital, excellent recoveries were obtained from well-defined conductance vs. volume plots. Results for the dicarboxylic phthalic and adipic acids were also good. However, the titration curves for the difunctional salicylic and p-hydroxybenzoic acids were not clearly defined. The results are discussed and compared with cnductometric titrations of acids in other non-aqueous solvents. Several determinations of electrolyte conductance as a function of concentration revealed that, as expected, the selected substances are weak electrolytes in methoxyethanol.