A 31P-NMR study on the recovery of intracellular pH in LLC-PK1/Cl4 cells from intracellular alkalinization

A perifusion loop-gap resonator NMR probe for aerobic cell suspensions

NMR studies of aerobic cell metabolism require that spectral data of high sensitivity and resolution be acquired from samples maintained under suitable conditions. The loop-gap resonator 31P NMR probe described here was designed for investigations of highly aerobic-dependent renal proximal tubules in an environment similar to those of conventional incubation flasks. The inherently higher sensitivity of the loop-gap resonator design and associated circuitry made it possible to obtain adequate spectra in short periods of time with small amounts of sample. Cellular physiological properties of perifused aerobic renal proximal tubule cell suspensions in the loop-gap resonator probe were found to be similar to equivalent tissue samples incubated in conventional flasks. Furthermore, the loop-gap perifusion probe was found to provide useful 31P NMR spectra of the kidney tubule system after acquisition times as short as 3 min.

The regulation of intracellular pH studied by 31P- and 1H-NMR spectroscopy in superfused guinea-pig cerebral cortex slices

(1) The intracellular pH (pHi) of superfused slices of guinea-pig cerebral cortex was measured in 31P-NMR spectra using the chemical shifts of intracellular inorganic phosphate (Pi) and of 2-deoxyglucose 6-phosphate (DOG6P). The pHi was found to be 7.30 +/- 0.04 (SD, n = 15) in bicarbonate-buffered medium and 7.20 +/- 0.05 (n = 10, P < 0.001) in bicarbonate-free HEPES buffer of the same pH (7.4). (2) Decreases in pHe below 7.05 resulted in pHi falling to similar values, with a decrease in the energy state. There was no change in intracellular lactate as assessed by 1H-NMR. (3) The tissues showed an ability to buffer higher pH: increasing pHe to 8.0 had no effect on pHi, PCr or lactate. (4) In order to characterize possible mechanisms of pH regulation in the tissue, the recovery from acid insult was investigated under various conditions. Initially pHi was decreased to 6.44 +/- 0.15 (n = 15) by exposure to media containing 6 mM bicarbonate gassed with O2/CO2, 80:20 (pHe 6.4). When this medium was replaced by normal bicarbonate buffer (pH 7.4) there was full recovery of pHi to 7.31 +/- 0.05 (n = 15), whereas replacing the buffer with HEPES resulted in incomplete recovery of pHi to 6.88 +/- 0.15 (n = 15, P < 0.001). (5) In the presence of the carbonic anhydrase inhibitor, acetazolamide (1 mM), or the sodium/proton exchange inhibitor, amiloride (1 mM), there was an incomplete return of pHi to the control value (pHi 6.90 +/- 0.20, n = 5, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

An NMR spectroscopic characterization of a new epithelial cell line, TALH-SVE, with properties of the renal medullary thick ascending limb of Henle's loop

NMR spectroscopy has been used to characterize a new renal cell line, TALH-SVE.1, which is derived from the medullary thick ascending limb of Henle's loop. From the 31P-NMR spectrum of a suspension of TALH-SVE cells using the chemical shift of the intracellular inorganic phosphate a value of 7.24 +/- 0.04 for the steady-state intracellular pH (pHi) was determined at pHo = 7.40. In addition, the 31P-NMR spectrum indicated rather high levels of UDPG, a finding confirmed by 1H-NMR spectra of perchloric acid extracts. The 1H-NMR data also demonstrate the presence of 'organic osmolytes' such as inositol, sorbitol, choline and glycerophosphoryl choline (GPC). 13C-NMR spectra of perchloric acid extracts of TALH-SVE cells incubated with [2-13C]- and [3-13 C]alanine were used to determine the relative influx in the Krebs cycle via pyruvate carboxylase (PCB) versus the influx via pyruvate dehydrogenase (PDH). The ratio was 0.41, while about 52% of all acetyl-CoA entering the Krebs cycle was unlabeled. 13C-NMR experiments also indicated that TALH-SVE cells lack gluconeogenic activity. The NMR study presented indicates that TALH-SVE cells possess metabolic pathways similar to those of the parental cells.

Cl-Cl exchange in promyelocytic HL-60 cells follows simultaneous rather than ping-pong kinetics

The intra- and extracellular chloride concentration dependencies of the rate of Cl-Cl exchange in human promyelocytic leukemic HL-60 cells were studied by means of radioactive isotope (36Cl) efflux measurements. Efflux of isotope from cells follows an exponential time course. The Cl-Cl exchange flux follows Michaelis-Menten kinetics as a function of both intra- and extracellular chloride concentrations. The ratio of the maximum exchange velocity to the apparent Michaelis constant for both extracellular and intracellular substrate increases as a function of trans Cl concentration, indicating that Cl-Cl exchange in the HL-60 cell does not follow ping-pong kinetics. A kinetic scheme in which extracellular and intracellular chloride ions bind in random order to the transporter and are then translocated simultaneously can adequately model the experimental data.

Polarity, diversity, and plasticity in proximal tubule transport systems

This contribution first reviews the distribution of transport systems within the plasma membrane of the proximal tubule cell (polarity), with particular emphasis on transport systems located in the basal-lateral plasma membranes and on the role of cascade coupling in tubular transport. Then, the differences between transport systems in the pars convoluta and the pars recta of the proximal tubule are discussed (diversity). Finally, evidence is presented that changes in the microenvironment of sodium cotransport systems can alter the mode of operation of the transporter (plasticity). The two examples mainly addressed are the sodium-D-glucose and the sodium-glutamate cotransport system.

Characterization of the renal epithelial cell line, PKE 5, using 31P- and 13C-NMR spectroscopy

In order to characterize intracellular pH regulation and cellular metabolism in PKE 5 cells, a mutant of the renal epithelial cell line LLC-PK1 supposed to lack Na+-H+ exchanger activity, 31P and 13C-NMR studies were conducted. The 31P studies on intact cell suspensions revealed that these cells have an ATP content and an ATP/ADP ratio similar to the parent cell line. Their intracellular pH, in the presence of 5 mM HCO3-, was 7.17 +/- 0.04 (n = 5) - identical to that of LLC-PK1 cells. After acid loading the cells with 15% CO2, the initial rate of realkalinization was 0.027 pH units/min (n = 6), 50% lower than in the parent cells. The recovery rate was not affected by the removal of extracellular sodium or by the addition of 1 mM amiloride. These results indicate that PKE 5 cells are devoid of Na+-H+ exchange activity, but are able to regulate their intracellular pH by amiloride-insensitive, sodium-independent mechanisms. Extracts prepared from PKE 5 cells incubated with [13C]lactate showed 13C spectra identical to those of the parent cell line. In particular, no synthesis of 13C-labeled D-glucose was observed.