Inertial picobalance reveals fast mass fluctuations in mammalian cells.

The regulation of size, volume and mass in living cells is physiologically important, and dysregulation of these parameters gives rise to many diseases. Cell mass is largely determined by the amount of water, proteins, lipids, carbohydrates and nucleic acids present in a cell, and is tightly linked to metabolism, proliferation and gene expression. Technologies have emerged in recent years that make it possible to track the masses of single suspended cells and adherent cells. However, it has not been possible to track individual adherent cells in physiological conditions at the mass and time resolutions required to observe fast cellular dynamics. Here we introduce a cell balance (a 'picobalance'), based on an optically excited microresonator, that measures the total mass of single or multiple adherent cells in culture conditions over days with millisecond time resolution and picogram mass sensitivity. Using our technique, we observe that the mass of living mammalian cells fluctuates intrinsically by around one to four per cent over timescales of seconds throughout the cell cycle. Perturbation experiments link these mass fluctuations to the basic cellular processes of ATP synthesis and water transport. Furthermore, we show that growth and cell cycle progression are arrested in cells infected with vaccinia virus, but mass fluctuations continue until cell death. Our measurements suggest that all living cells show fast and subtle mass fluctuations throughout the cell cycle. As our cell balance is easy to handle and compatible with fluorescence microscopy, we anticipate that our approach will contribute to the understanding of cell mass regulation in various cell states and across timescales, which is important in areas including physiology, cancer research, stem-cell differentiation and drug discovery.

High-resolution mass measurements of single budding yeast reveal linear growth segments.

The regulation of cell growth has fundamental physiological, biotechnological and medical implications. However, methods that can continuously monitor individual cells at sufficient mass and time resolution hardly exist. Particularly, detecting the mass of individual microbial cells, which are much smaller than mammalian cells, remains challenging. Here, we modify a previously described cell balance ('picobalance') to monitor the proliferation of single cells of the budding yeast, Saccharomyces cerevisiae, under culture conditions in real time. Combined with optical microscopy to monitor the yeast morphology and cell cycle phase, the picobalance approaches a total mass resolution of 0.45 pg. Our results show that single budding yeast cells (S/G2/M phase) increase total mass in multiple linear segments sequentially, switching their growth rates. The growth rates weakly correlate with the cell mass of the growth segments, and the duration of each growth segment correlates negatively with cell mass. We envision that our technology will be useful for direct, accurate monitoring of the growth of single cells throughout their cycle.

Sleep complaints: snoring and daytime sleepiness in pregnant and pre-eclamptic women.

BACKGROUND AND PURPOSE: To examine whether snoring and sleepiness are linked in pregnancy and pre-eclampsia. PATIENTS AND METHODS: We recruited 167 healthy and 82 pre-eclamptic women in the third trimester of pregnancy and 160 non-pregnant women. Subjects and their partners completed a sleep questionnaire. Height, weight, neck circumferences and blood pressure were recorded for all. RESULTS: Pregnant and pre-eclamptic women were (mean +/-SD) 36+/-3.6 and 36+/-3 weeks pregnant, respectively. Age and height did not differ significantly between groups (P>0.2), but pre-eclamptic women were heavier than pregnant and non-pregnant women and had higher BMI than pregnant women before pregnancy (all P<0.05). Thirty-two percent of control, 55% of pregnant and 85% of pre-eclamptic women snored (P<0.001), but pre-pregnancy snoring rates (pre-eclamptic=36%, healthy pregnant women=27%) were similar to those in non-pregnant women (32%) (P>0.7). Sleepiness was reported by 12% of non-pregnant, 23% of pregnant and 15% of pre-eclamptic women (P<0.04), but non-pregnant women had lower mean Epworth Sleepiness scores than both pregnant and pre-eclamptic groups (P<0.001). Snoring was correlated with (P=0.002), but explained only <2%, of the variance in sleepiness. CONCLUSION: Snoring and sleepiness increased in the third trimester of pregnancy, particularly in patients with pre-eclampsia. However, the study suggests that sleepiness in pregnancy is largely due to factors other than snoring or breathing pauses.

The upper airway in pregnancy and pre-eclampsia.

Snoring is common in pregnancy, and snoring pregnant women have increased rates of pre-eclampsia. Patients with pre-eclampsia show upper airway narrowing during sleep. The present study aimed to compare upper airway dimensions in pregnant and nonpregnant women and in patients with pre-eclampsia. A total of 50 women in the third trimester of pregnancy and 37 women with pre-eclampsia were recruited consecutively from the antenatal service and matched with 50 nonpregnant women. Upper airway dimensions were measured using acoustic reflection. Comparisons were made by analysis of variance and Student-Newman-Keuls tests. Snoring was reported by 14% of nonpregnant women, 28% of pregnant women, and 75% of pre-eclamptic women (p < 0.001). When seated, pregnant women had wider upper airways than nonpregnant women (p < 0.02), but there was no difference when supine. Oropharyngeal junction area in the seated position was less (p < 0.01) in the women with pre-eclampsia (mean +/- SD: 0.9 +/- 0.1 cm2) than either nonpregnant (1.1 +/- 0.1 cm2) or pregnant women (1.3 +/- 0.1 cm2). Supine oropharyngeal junction area was less in the women with pre-eclampsia than in the nonpregnant women (0.8 +/- 0.1 versus 1.0 +/- 0.1 cm2; p = 0.01) but similar in women with pre-eclampsia and pregnant women (0.9 +/- 0.1 cm2; p > 0.3). The study showed that women with pre-eclampsia have upper airway narrowing in both upright and supine postures. These changes could contribute to the upper airway resistance episodes during sleep in patients with pre-eclampsia, which may further increase their blood pressure.