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L Kampmann

Publications and source records attributed to L Kampmann.

6 recordsLinked to original sources
PubMed1982

Square wave pulse analysis of cellular and paracellular conductance pathways in Necturus gallbladder epithelium.

In search for a rapid and reliable method to identify and quantitatively determine cell membrane resistances and paracellular shunt resistances in epithelia we have developed appropriate techniques to measure transepithelial and intracellular potential transients in response to transepithelially applied square wave constant current pulses. Model considerations indicate that in a unilayered, homogeneous epithelium with open lateral spaces the transient potential response across each cell membrane should obey a single exponential function in case the tight junction resistance is high, as in a tight epithelium, whereas in a leaky epithelium it should consist of a superposition of two exponentials with equal sign at the membrane with the higher intrinsic time constant and of two exponentials of different sign (overshoot with recline) at the membrane with the lower intrinsic time constant. The latter predictions were experimentally verified in a study on Necturus gallbladder epithelium and equivalent circuit parameters for the cell membrane resistances and capacitances as well as for the resistance of the shunt path were calculated from the data by curve fitting procedures. The resistances of the apical and basal cell membrane and of the shunt path averaged 1220, 201 and 91 omega cm2 respectively while the apical and basal cell membrane capacitances were 8.0 and 26.3 micro F/cm2 respectively. The fact that the resistance values are 4-15 times lower than estimates derived previously from 2D-cable analysis relates to a better preservation of the transport function under the present incubation conditions as verified by a new series of cable analysis data. The capacitances agree well with estimates of the surface amplification of the cell membranes from electronmicrographs, thus confirming the validity of the interpretation of the observed voltage transients.

Animals↗
PubMed1982

The kinetics of intramolecular cross-linking of the band 3 protein in the red blood cell membrane by 4,4'-diisothiocyano dihydrostilbene-2,2'-disulfonic acid (H2DIDS).

The two isothiocyanate groups of the anion transport inhibitor 4,4'-diisothiocyano dihydrostilbene-2-2'-disulfonate (H2DIDS) may react covalently with two lysine residues called a and b that reside on the chymotryptic 60,000 Dalton and 35,000 Dalton segments, respectively, of the band 3 protein of the human erythrocyte membrane. Under suitable conditions, the reaction leads to the establishment of intramolecular cross-links between a and b (M.L. Jennings & H. Passow, 1979, Biochim. Biophys. Acta 554:498-519). In the present work, the time course of the reactions with a and b, and of the establishment of the cross-link were investigated experimentally and compared with simple mathematical models of the reaction sequence. The rates of reaction with a and b were found to increase with increasing pH. Regardless of pH, the rate of reaction with a exceeds that with b several-fold. Once the H2DIDS molecule has reacted with a, the rate of the subsequent reaction of the other isothiocyanate group with b is reduced by about 1/30. The reactions that follow the unilateral attachment to site b are not yet clear. A more detailed analysis of the time course of the cross-linking reaction suggests that a satisfactory description of the kinetics requires the assumption that the H2DIDS binding site may exist in two different states, and that the transition from one state to the other is associated with changes of the reactivities of either lys a alone or of both lys a and b. This led to the formulation of the two-states model of the H2DIDS binding site, which is supported by other pieces of independent evidence. The analysis of the pH dependence of the rate of thiocyanylation of b shows that the apparent pK value of that lysine residue is about 9.9 to 10.0 and hence slightly lower than the intrinsic pK of a lysine residue in an aqueous environment.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗