Morgan Sohtell

The determination of bicarbonate in nanoliter samples.

Abstract A methodological system is described which permits the determination of bicarbonate ions in samples of a few nanoliters. The samples were collected anaerobically and were then equilibrated in oil of different CO2 tensions. The pH was measured with antimony microelectrodes after each equilibration. The pH log , PCO2 curve thus obtained represented the buffer curve. Using the intratubular pH measured in situ prior to the sampling, the corresponding PCO2 was obtained from the buffer curve. Using the Henderson-Hasselbalch equation, the bicarbonate concentration was calculated for that particular PCO2. Some theoretical and practical aspects on these determinations are discussed.

In vivo micropuncturePCO2 measurements

SummaryAn electrode is presented which permits in vivoPCO2 measurements using a micropuncture technique. The tip diameter of the electrode is only a few microns, the tip is specially designed for measuringPCO2 in small tissue compartements.

The Determination of Ultrafiltrable Calcium and Magnesium in Serum

Ultrafiltrate of human serum was investigated in order to evaluate the serum content of calcium and magnesium. The acid and base concentrations and pH of the serum was altered through titration with HCl- or NaOH-solutions. The Pco2 was varied in the titrated serum using different carbon dioxide tensions. This was performed when serum was filtered in a recycling system. It is shown that the analysis of calcium and magnesium have to be done under anaerobic conditions or at standardized pH and Pco2 situations, as the concentrations vary with both pH and Pco2. The concentration ratio between ultrafiltrate and serum for calcium and magnesium was found to be 0.56 and 0.74 respectively at pH=7.41 and Pco2=40 mmHg.

Microelectrode studies of D-glucose- and K+-induced changes in membrane potential of electrofused insulin-producing cells

In the present study electrical field‐induced fusion has been applied to both normal pancreatic islet cells isolated from obese hyperglycemie mice and clonal insulin‐producing cells (RINmSF) derived from a transplantable rat insulinoma. The fused cells were then punctured with microelectrodes to measure changes in membrane potential after exposure to stimulatory concentrations of D‐glucose or K+. Fused cells of normal islet cellular origin revealed a resting membrane potential of −60 mV and were depolarized by 24 or 27 mV after exposure to 11 mM D‐glucose or 30 mM K+. Although D‐glucose induced depolarization, it was not possible to establish the existence of an oscillating burst pattern superimposed by action potentials. The resting membrane potential of the fused RINm5F cells was also −60 mV and decreased to −30 mV after exposure to 30 mM K+. As judged from the membrane potential measurements, the reconstitution of the plasma membrane subsequent to electrical breakdown is essentially the same whether the giant cells originated from normal islet cells or RINm5F cells.

Beta-2-Microglobulin Excretion in Renal Stone-Formers

Renal tubular defects in patients with recurring kidneystones have not been paid much attention to, except in patients with RTA. In order to investigate the proximal tubular function in renal stone formers the excretion of beta-2-microglobulin was measured under different conditions.