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T Zeuthen

Publications and source records attributed to T Zeuthen.

69 records · Page 4Linked to original sources
PubMed1978

An electrogenic NA+/K+ pump in the choroid plexus.

Intracellular electrical potential and potassium activity was measured by means of microelectrodes in the epithelial cells of choroid plexus from bullfrogs (Rana catesbeiana). Ouabain applied from the ventricular side caused an abrupt depolarisation of 10 mV but only a gradual loss of potassium from the cells. Readministration of potassium to the ventricular solution of plexuses which were previously depleted of potassium, caused a hyperpolarisation of about 4 mV. These two experiments are consistent with the notion of an electrogenic Na+/K+ pump situated at the ventricular membrane and which pumps potassium into the cell and sodium into the ventricle. The numerical values obtained suggest that 3 sodium ions are pumped for 2 potassium ions. The permeability coefficient for potassium exit from the cell is calculated to be 1.24 . 10(-5) cm-1 . s-1 expressed per cm2 of flat epithelium.

Animals↗
PubMed1978

Intracellular gradients of ion activities in the epithelial cells of the Necturus gallbladder recorded with ion-selective microelectrodes.

In Necturus gallbladder epithelial cells the intracellular electrical potential, as recorded with microelectrodes, varied from -28 mV in the mucosal end to about -50 mV in the serosal end of the transporting cell. The Na+ activity varied concurrently from about 39 mM to between 8 and 19 mM. Thus, within the cell both the recorded electrical and chemical gradients caused Na+ to move towards the serosal end. Serosal addition of ouabain (5 X 10(-4) M) caused the intracellular Na+ activity to attain electrochemical equilibrium within 30 min. However, the intracellular electrical potential gradient was only slowly affected. In cells from animals stored at 5 degrees C, the Cl- activity varied from about 55 mM in the mucosal end to 28 mM in the serosal end, and the K+ activity from 50 mM to between 95 and 131 mM. Both ions were close to electrochemical equilibrium within the cytoplasm but were too concentrated to be in equilibrium with the mucosal solution. Bubbling CO2 through the mucosal solution caused the intracellular gradients to vanish. When Na+ in the bathing solutions was exchanged for K+, the intracellular electrical potential became roughly constant at about -5 mV. The Cl- activity became constant in 65 mM, and the K+ activity became constant at 109 mM, both close to equilibrium with the mucosal solution. The Na+ activity was reduced to about 1 mM. The ratio of cytoplasmic resistivities between cells bathed in K+-rich saline to cells bathed in Na+-rich saline was measured by means of triple-barreled electrodes and compared to the same ratio as assessed from the activity measurements. The two values were equal only if one assumes the mobility of Na+ inside the cell to be less than 1/10 of the mobility of K+ or Cl-. The same conclusion was reached by comparing the intracellular Na+ flux calculated from the gradient of electrochemical potential to that flux assess from the net solute absorption. Animals kept at 15 degrees C had lower intracellular Na+ activities, higher Cl- and K+ activities, and higher rates of absorption than animals stored at 5 degrees C. Finally, the degree to which the intracellularly recorded electrical and chemical potentials could reflect an electrode artefact is discussed.

Animals↗
PubMed1977

Intracellular gradients of electrical potential in the epithelial cells of the Necturus gallbladder.

When single-barrelled electrodes (5-60 Momega) were advanced under manual control from the mucosal side of the epithelium the mucosal membrane was on average indented by about 40 micron before the microelectrode pentrated the cell. Since this dimpling was comparable with the total depth of the cell, which recovered its original shape within 0.5 sec, the steady intracellular potential was recorded only about 14 micronm from the basal (serosal) membrane. Fast recording of the associated change in potential revealed an abrupt drop to -26 mV at a mean rate of 84 V/sec, followed by a further slow drop to a steady value of about -50 mV at a mean rate of 0.28 V/sec. The initial level of -26 mV may be regarded as the potential difference across the mucosal membrane. This conclusion was confirmed by mounting the microelectrode on a piezoelectric probe, which delivered 3 micron jabs in less than 0.5 msec. With this device in operation to prevent dimpling, the mean potential difference across the mucosal membrane was recorded as -29 mV. In all cases the potential across the basal membrane was recorded as -52 mV. Manual advance of the microelectrode tip within the cytoplasm yielded an intracellular potential gradient of 0.6 mV/micron. The same potential profile and membrane potentials were demonstrated on penetrating the epithelium from the serosal side, and measurements with multibarrelled electrodes whose tips were staggered in depth gave roughly the same internal potential gradient. The resistivity of the cytoplasm was determined by a triple-barrelled microelectrode, and varied from 10 times that of Necturus saline at the mucosal end of the cell to 4 times in the middle and 6 times at the serosal end.

Animals↗