Electron probe X-ray microanalysis of intracellular element concentrations in cryosections in the presence of changes in cell volume.

The interpretation of element concentration data for X-ray microanalyses of biological tissues, which are subjected to some experimental treatment, can be complicated by changes in cell volume and total cell dry matter induced by the treatment. We have examined the manner in which such changes would affect the values measured in frozen-dried cryosections of soft tissues, and how they may be taken into account in the interpretation of the results. The element content (mass per unit dry weight) measured by the peak-to-continuum or Hall method is independent of changes in cell volume, but is sensitive to a change in the local dry mass. Conversely, intracellular concentrations in terms of mass per unit volume, as determined by the peripheral or internal standard technique, are dependent on volume changes but independent of dry mass. The estimated dry weight fraction is affected by changes in both volume and dry mass. The results obtained from both quantification methods can therefore provide information on the combination of changes in cellular element levels, volume and total dry mass that may occur following the experimental treatment. In a study of the late effect of the drug cisplatin on electrolyte concentrations in kidney proximal tubules, both quantification methods have been used to obtain wet weight and dry weight concentrations. By applying the above considerations, the analytical results have been interpreted as a combination of changes in element levels and a shrinkage of the tubule cells. Cell shrinkage was confirmed by morphometric analysis of tubular cross-sections

Acute cisplatin nephrotoxicity in the rat. Evidence for impaired entry of sodium into proximal tubule cells.

The earliest phase of cisplatin nephrotoxicity involves natriuresis due to impaired sodium reabsorption by the proximal tubule. To define the cell mechanism of this transport lesion, electron microprobe X-ray analysis was used to determine changes in the electrolyte composition of proximal tubule cells in kidneys taken from rats treated acutely with cisplatin (1 mg/100 g body weight). Compared to control animals injected with vehicle, cisplatin treated rats developed significant natriuresis, the fractional excretion of sodium rising over sevenfold. In kidneys removed 90 min following cisplatin, sodium concentration in proximal tubule cells was reduced by 4.2 mmol/kg wet weight, or 19%, compared to control values. When allowance was made for cell shrinkage in cisplatin-treated kidneys by deriving the cell content of sodium (mmol/kg dry weight), the reduction was even greater (28%). These data suggest that cisplatin reduces proximal tubule sodium reabsorption by inhibiting the entry of sodium into the cells across the apical membrane

Effect of atrial natriuretic peptide on cellular element concentrations in rat proximal tubules: evidence for inhibition of the sodium pump.

1. In order to further define the action of atrial natriuretic peptide (ANP) on proximal tubular (PT) transport, combined clearance and electron microprobe X-ray (EMPX) experiments were performed on five male Wistar rats infused with ANP (0.16 nmol/kg per h) and nine control animals. 2. Electron microprobe X-ray analysis of PT cell electrolytes (mmol/kg wet weight) revealed a similar [Na]i in both the control and ANP treated groups (16.4 +/- 0.4 vs 16.5 +/- 0.4; P = 0.894). [Cl]i was lower in the ANP treated animals (14.8 +/- 0.3 vs 12.0 +/- 0.3; P < 0.0001) as was [K]i (131.4 +/- 1.4 vs 114 +/- 1.7; P < 0.0001). The PT cells in the ANP treated group had a significant reduction in dry weight (20.1 +/- 0.3 g% vs 19.0 +/- 0.3 g%; P < 0.024), indicating significant cell swelling. Thus, despite a normal [Na]i, there was net accumulation of Nai following ANP treatment. 3. These results are consistent with accumulation of Nai due to inhibition of the Na pump followed by cell swelling and subsequent regulatory volume decrease with exit of K and Cl. These results are the first to show the effect of ANP on PT intracellular electrolytes