The uptake of non-metabolizable amino acids as an index of cell viability in vitro

A cytotoxicity assay utilizing a fluorescent dye that determines accurate surviving fractions of cells

A cytotoxicity assay has been developed based on the measurement of the proliferative activity of surviving cells as quantified by a cell-incorporated fluorescent dye, 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The BCECF proliferative assay is fast (the results are obtained within 3-4 days depending on the cell line), accurate, not labor-intensive, does not require the use of radioisotopes or toxic compounds, and is amenable to automation. The BCECF proliferative assay was compared with two other indirect cytotoxicity tests, a trypan blue exclusion test and a BCECF viability test. Neither of these two latter assays reflected in any way the killing of cells by ricin. In contrast, using the BCECF proliferation assay, an optimal period of cell culturing after exposure to a toxin could be found so that the cytotoxicity values produced agreed with the surviving fractions of cells measured in a direct cytotoxicity assay. Under non-optimal conditions, the assay reflected the cell kill only qualitatively. Although it is common practice to conduct indirect cytotoxicity tests without validating them with a direct assay, our experiments demonstrate that the values obtained in such non-optimized indirect cytotoxicity tests may not parallel the cell kill and may, therefore, be meaningless.

Bioelectric activity as a quantifiable index of acute spermicide (nonoxynol-9) actions on rat vaginal epithelial function during the oestrous cycle

The acute effect of instillation of the spermicide 2% nonylphenoxypolyethoxyethanol (nonoxynol-9) on the bioelectric activity of the vaginal epithelium was assessed using as an index the time taken in seconds to reduce the transvaginal potential difference (p.d.), measured in anaesthetised rats, to half its initial value (t1/2). The surfactant caused rapid falls in the p.d. at dioestrus (t1/2 = 35 +/- 25 sec., n = 16, mean +/- S.D.) and metoestrus (t1/2 = 32 +/- 27 sec., n = 11) with a slower fall at oestrus (t1/2 = 130 +/- 104 sec., n = 14). At pro-oestrus however, nonoxynol-9 had no effect (n = 18). The dye Nigrosin (0.5%), when instilled alone, did not stain untreated vaginas of anaesthetized rats at any stage of the oestrous cycle, but in the presence of 2% nonoxynol-9 heavily stained those in metoestrus and dioestrus. Vaginas in pro-oestrus were unstained while those in oestrus were stained lightly. While nonoxynol-9 has a dramatic effect on the bioelectric activity of the vaginal epithelium, both the electrical and dye data show that the pro-oestrus vaginal epithelium presents a significant diffusion barrier to the passage of nonoxynol-9 and nigrosin. Thus, in assessing the actions of vaginally instilled nonoxynol-9 in rats the variation in the permeability of the vaginal epithelium during the oestrous cycle must be taken into account.

Induction of taurocholate release from isolated rat hepatocytes in suspension by alpha-adrenergic agents and vasopressin: implications for control of bile salt secretion

Hepatocytes incubated with 25 muM [3H] taurocholate rapidly deplete the extracellular medium of [3H] taurocholate and achieve a steady-state level of intracellular bile salt within 15 min. Exposure of cells at steady state with extracellular taurocholate to the catecholamines norepinephrine or epinephrine results in release of 3H from the cells into the incubation medium; the 3H released represents almost exclusively unmetabolized [3H] taurocholate. The hierarchy of effectiveness of the catecholamines, norepinephrine congruent to epinephrine greater than phenylephrine much greater than isoproterenol, is indicative of an alpha-adrenergic mechanism. Induction of [3H] taurocholate release by norepinephrine is inhibited by the alpha-antagonists phenoxybenzamine and phentolamine and by chlorpromazine, but is not affected by the beta-antagonist propranolol, further supporting an alpha-adrenergic basis for this phenomenon. Arginine vasopressin, at concentrations of 1 X 10(-9) M and greater, also induces bile salt release. Classical alpha- and beta-antagonists have minimal effects on vasopressin induced bile salt release. While the peptide hormones angiotensin and oxytocin are, alone, relatively ineffective inducers of bile salt release, oxytocin potentiates the induction of bile salt release by vasopressin, suggesting complex interactions with membrane receptor function. Further studies assessing the interaction of sympathetic neurotransmitters and peptide hormones with bile salt transport and release in the hepatocyte may provide insight into the regulation of hepatic secretory function in the intact animal.

Deleterious effects of calcium deprivation on freshly isolated hepatocytes

Biochemical and morphological properties of rat hepatic parenchymal cells isolated without calcium were compared to cells isolated by adding calcium to the isolation medium at the time of addition of collagenase. Calcium contents of the two cell preparations were 4.5 +/- 0.3 and 10.5 +/- 0.5 nmol/mg dry wt, respectively (P les than 0.001). Magnesium content of both preparations was 37 nmol/mg dry wt. Potassium contents were 92 and 154 meq/l, respectively (P less than 0.001). Potassium content of calcium-deficient cells increased to 161 meq/l following incubation for 30 min in a medium containing 1.6 mM ionized calcium. When incubated in a medium containing a subphysiologic concentration of ionized calcium, calcium-deficient cells rapidly lost the ability to exclude trypan blue and to retain lactate dehydrogenase activity. As contrasted to calcium-sufficient hepatocytes, calcium-deficient cells failed to accumulate alpha-aminoisobutyric acid by active transport and lacked microvilli and nuclear contents. This study supports simultaneous addition of calcium and collagenase to the isolation medium as a means for preserving physical, functional, and morphological integrity of isolated hepatic parenchymal cells.

Evaluation of methods for determining 6-hydroxydopamine cytotoxicity

The toxic effects of 6-hydroxydopamine on the human neuroblastoma cell line SK-N-SH-SY5Y(SY5Y) and the Chinese hamster ovary (CHO) cell line were measured with five viability assays. Four of the assays (attachment efficiency, plating efficiency, amino acid incorporation into acid-precipitable proteins, and Trypan Blue dye exclusion) showed higher drug susceptibility in SY5Y cells than CHO cells. Only growth inhibition (proliferation index) gave results indicating greater sensitivity in CHO cells. Over a time span of 48 hr, injured cell populations lost vital functions in the following order: attachment ability, amino acid incorporation, proliferative capacity, and dye exclusion. Recovery of each of the functions occurred in sublethally injured populations. Monitoring the extinction and recovery of vital functions permitted the accurate determination of a drug concentration (30 micrograms/ml) selectively toxic for SY5Y cells. A strong correlation was noted between relative values for amino acid incorporation 3 hr after drug treatment, attachment efficiency at 24 hr, and dye exclusion at 24 and 48 hr. We concluded that Trypan Blue dye exclusion and amino acid incorporation were suitable methods for comparing the effects of cytotoxins on different cell lines, provided they were performed at the appropriate time after treatment with the toxin. The combined techniques yield both population and individual cell data, are simple to do, and are applicable to nondividing cell populations.

Energetics of amino acid transport into brain slices: effects of glucose depletion and substitution of Krebs' cycle intermediates

Amino acid uptake by slices of brain is greatly diminished by incubation of the slices in glucose-free media. Uptake can be restored by the addition of a number of substrates, e.g., lactate, citrate, or oxaloacetate. The mixture of succinate, malate, and pyruvate (SMP, 20, 5, and mM) restored amino acid uptake better than glucose after brain slices were incubated in glucose-free media to deplete endogenous energy stores. The degree of restoration of uptake was different with the various amino acid transport classes and was independent of the restoration of ATP levels in the tissue. After restoration of uptake with SMP the amino acid uptake was resistant to NaF, but was markedly more sensitive to arsenite and oligomycin. The results indicate the coupling of mitochondrial energy transducing systems to transport.

Isotope-labelled alpha-amino-isobutyric acid as an indicator in cytotoxicity tests

The effect of rabbit antisera on the uptake and release of alpha-amino-isobutyric acid (AIBA) in LS- and P-388 cells was investigated. In the presence of homologous antiserum and complement, the uptake of AIBA was inhibited. In the absence of complement, no effect of antiserum was seen. Using prelabelled cells, the efflux of AIBA was greatly accelerated in the presence of antiserum and complement. The AIBA-uptake method was compared with the trypan blue exclusion test and the 51Cr release technique. The AIBA-uptake method was more sensitive in quantitative cytotoxic studies.

Comparison of some permeability properties of rat liver slices, liver cells in suspension, and in vivo-produced aggregates of dispersed liver cells

It has been reported earlier that when rat liver is dispersed to a single cell suspension, the parenchymal cells lose the ability to take up pyrimidine bases but acquire the ability to take up RNAase and macromolecular nucleic acids. It is now shown that these changes are largely reversed on intraperitoneal reaggregation of the parenchymal cells and that, in these respects, the aggregates behave more like the organized tissue than like the dispersed cells.

Effect of cell concentration on the uptake of amino acids by rat liver parenchymal cells in suspension

The accumulation of several amino acids in the acid-soluble fraction and their incorporation into protein in rat liver parenchymal cell suspensions, has been shown to depend on the concentration of cells in the incubation medium; the uptake, both in the acid-soluble and the acid-insoluble fractions, decreased as the cell concentration increased from 0.03 X 10(6) cells/ml upwards, reaching a plateau at high cell concentrations (3-5 X 10(6) cells/ml). The uptake values at high cell concentrations were the same as those obtained in liver slices in which a similar effect was not observed. Evidence is presented which suggests that this phenomenon is mediated by a material released from the cells in suspension, which is inhibitory to enhancement of the uptake of amino acids by these cells over and above the value obtained in normal, adult liver slices.

The selective inhibitory effect of hyperthermia on the metabolism and growth of malignant cells

Hyperthermia (42° C.) exerted an inhibitory effect on the O(2) uptake of rabbit VX2 carcinoma cells in vitro, and led to a decrease in viability and growth potential of the cells, as measured by their ability to produce tumours in rabbits. Anaerobic glycolysis of the tumour cells was unaltered by hyperthermia. Respiration and anaerobic glycolysis of normal rabbit liver, kidney and red blood cells were unaffected by the elevated temperature. Local heat was applied to established VX2 tumours in vivo, with a subsequent reduction in tumour size in all cases, the most effective therapy regime being 3 one-hour applications of heat within the mean cell generation time of the tumour. Following heating there was rapid and widespread tumour cell necrosis and lysis, with subsequent replacement of the tumour architecture by connective tissue. There was a prolongation of survival time in 50% of the treated animals, which are still alive 18 months after therapy; all the control animals died within 10 weeks. The selective inhibitory effects of hyperthermia on cancer cells, and its application to human neoplasms, are discussed.