Recent work on selected aspects of the cellular and molecular physiology of cell volume regulation is reviewed. First, the physiological significance of the regulation of cell volume is discussed. Membrane transporters involved in cell volume regulation are reviewed, including volume-sensitive K + and CI − , channels, K + , CI − and Na + , K + , 2CI − cotransporters, and the Na + , H + , CI − , HCO 3 − , and K + , H + exchangers. The role of amino acids, particularly taurine, as cellular osmolytes is discussed. Possible mechanisms by which cells sense their volumes, along with the sensors of these signals, are discussed. The signals are mechanical changes in the membrane and changes in macromolecular crowding. Sensors of these signals include stretch-activated channels, the cytoskeleton, and specific membrane or cytoplasmic enzymes. Mechanisms for transduction of the signal from sensors to transporters are reviewed. These include the Ca 2+ -calmodulin system, phospholipases, polyphosphoinositide metabolism, eicosanoid metabolism, and protein kinases and phosphatases. A detailed model is presented for the swelling-initiated signal transduction pathway in Ehrlich ascites tumor cells. Finally, the coordinated control of volume-regulatory transport processes and changes in the expression of organic osmolyte transporters with long-term adaptation to osmotic stress are reviewed briefly.

Membrane mechanisms and intracellular signalling in cell volume regulation.

This review compares published surveys of microbial populations in plant tissue and cell cultures with the microbial saprophytes and pathogens found on field grown plants and microbial populations in the laboratory environment. From this comparison and the measured reduction in contamination after improvements in working practices in the laboratory, conclusions can be drawn about the importance of the explant and the laboratory as sources of contamination. Mechanisms of pathogenicity in vitro are described to explain why bacteria, fungi, and yeasts that are not pathogenic to plants in the field become pathogens in plant tissue cultures. Conversely, plant metabolism and its effect on the tissue culture environment are described to explain why prokaryotes, viruses, and viroids that cause disease in the field can stay latent in vitro. Detection methods for latent contaminants in plant tissue cultures are summarized, and the strategies and methods for prevention or treatment of contamination are disc...

Ecology of Microbial Saprophytes and Pathogens in Tissue Culture and Field-Grown Plants: Reasons for Contamination Problems In Vitro

The aim of this study was to assess the relative validity of a 159-item semiquantitative food frequency questionnaire (FFQ) for use among adult Singaporeans. This FFQ should be able to classify intakes of energy, total fat, saturated fat, polyunsaturated fat, monounsaturated fat and cholesterol into quintiles of intakes for purposes of epidemiological studies. A total of 126 subjects (84 women and 42 men) took part in the study which included an interview using the newly developed FFQ (assess past month’s intake) and three 24-h (24 h) recalls (reference method, collected over a period of 1 month). Subjects also collected two 24 h urinary samples for urea from which total nitrogen excretion was assessed to validate protein intake. When compared to the reference method, the FFQ slighty overestimated the intakes of energy, total fat and types of fat as reflected by the difference in means and the ratio of FFQ to 24 h intakes. The overestimation ranged from 1 to 11% of the reference method. Dietary cholesterol was underestimated by 17% by the FFQ. These differences were however, not statistically significant. Pearson’s correlation coefficients (95% confidence intervals (CI)) between intakes assessed by FFQ and reference method varied from 0.58 (0.45, 0.69) for total fat to 0.39 (0.23, 0.53) for polyunsaturated fat. Cross-classification into quintiles resulted in correct classification into the same or adjacent quintiles in 70% of subjects, with only one or two subjects being grossly misclassified. Nitrogen (N) intake from the 24 h recalls did not differ significantly from that estimated from the urinary nitrogen excretion. The mean (± SD) difference was 0.0 ± 0.4 g and the Pearson correlation coefficient (95% CI) was 0.55 (0.31, 0.72). It is concluded that the newly developed FFQ is an adequate tool for classifying individuals’ intakes into quintiles for epidemiological studies among Singaporean adults.

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Validation of a semiquantitative food frequency questionnaire for estimation of intakes of energy, fats and cholesterol among Singaporeans

Tricyclic antidepressants are among the commonest causes of both non-fatal and fatal drug poisoning in the world. Their toxicity is due to effects on the brain, the heart, the respiratory system and the parasympathetic nervous system. Symptoms usually appear within 4 hours of an overdose and all but the most seriously poisoned patients recover within 24 hours. The most common clinical features are dry mouth, blurred vision, dilated pupils, sinus tachycardia, pyramidal neurological signs, and drowsiness. In severe poisoning, there may be coma, convulsions, respiratory depression, hypotension and a wide range of electrocardiographic (ECG) abnormalities. The most frequent findings on the ECG are prolongation of the PR and QT intervals; the tracing may resemble bundle branch block or supraventricular or ventricular tachycardias.

Poisoning due to tricyclic antidepressant overdosage. Clinical presentation and treatment.

After an initial 2-h incubation with phagocytic cells, the growth of surviving intracellular Staphylococcus aureus was examined in the presence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin One-tenth of the minimal inhibitory concentrations of these antibiotics markedly reduced bacterial growth in normal polymorphonuclear leukocytes In contrast, when human alveolar macrophages were studied, no inhibition of growth was seen Subinhibitory concentrations of these antibiotics and polymorphonuclear leukocytes acted synergistically to reduce intracellular survival of S aureus This synergy did not appear to be dependent upon the microbicidal potential of the leukocyte respiratory burst, since no differences were found when polymorphonuclear leukocytes obtained from patients with chronic granulomatous disease were compared with those from normal donors

Influence of subinhibitory concentrations of penicillin, cephalothin, and clindamycin on Staphylococcus aureus growth in human phagocytic cells.

Hypophosphatasia is an inherited metabolic disorder of bone, in which the underlying detect is a deficiency of bone alkaline phosphatase (Rathbun, 1948). Although Nadler (1968) showed that cultured human fetal cells express alkaline phosphatase activity, this has not been applied to the prenatal diagnosis of hypophosphatasia. We have recently been able to detect two cases of the congenital lethal form of hypophosphatasia prenatally in unrelated families. Amniotic fluid was obtained by transabdominal amniocentesis at about 16 weeks of gestation from patients, both of whom had had previous children who had succumbed to hypophosphotasia in the neonatal period. Cells were collected and cultured for three weeks, in parallel with cells ti'om controls wl-/o had amniocentesis performed for other clinical indications at about the same stage of gestation. The cells were harvested and washed twice with saline, and then homogenized by ultrasonic disruption. Alkaline phosphatase activity was measured with 4-methylumbelliferyl phosphate as substrate, the increase in fluorescence being determined with a recording fluorimeter. Compared with controls, alkaline phosphatase activity was low in cells from both patients at risk (Rattenbury et al. (1975) (Figure 1~. 6 0 0

Prenatal detection of hypophosphatasia: cytological and genetic considerations.

Letter: Prenatal diagnosis of hypophosphatasia.

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Prenatal detection of hypophosphatasia: cytological and genetic considerations.

Letter: Prenatal diagnosis of hypophosphatasia.