Flow cytometric analysis of the recruitment of G0 cells in human epidermis in vivo following tape stripping

Tape stripping of human skin elicits a proliferative response of a synchronously-dividing group of cells. The progress of this cohort of cells has been monitored using two windows in the cell cycle, one located in mid-S phase and the other centred around G2 + M. The cellular DNA is measured with flow cytometry, the windows are defined by two ranges in the DNA histogram. The cohort can be described as the recruitment of cells from a pre-existing G0 compartment which consists of 76% of all proliferative cells. The duration of the S phase is calculated to be 10.2 hr and G2 + M phase 5.1 hr. The cell cycle time of 39 hr for normal human keratinocytes derived from these figures is in line with recent values obtained by different techniques.     

Ratiometric measurement of intracellular pH in cultured human keratinocytes using carboxy-SNARF-1 and flow cytometry

In this study we describe a method to measure intracellular pH in cultured human keratinocytes using flow cytometry. Keratinocytes pose a technical problem because the population is heterogeneous with respect to size and metabolic activity (nonspecific esterase activity), resulting in variability in dye uptake. In order to compensate for this, dyes were selected that change colour with pH. The ratio of fluorescence intensities at two wavelengths was recorded and used as a measure of intracellular pH by reference to the pH in the presence of the proton ionophore nigericin. However, methods published till now do not routinely combine the ratiometric technique and excitation with an argon ion laser set at 488 nm. Therefore we have tested the recently developed pH-sensitive dye carboxyseminaphthorhodafluor-1 (SNARF-1) as a possible candidate for flow cytometric pH measurements and compared it with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) and 2,3-dicyanohydroquinone (DCH) with respect to emission spectra, resolution, range, and stability of cellular fluorescence. SNARF-1 had a practical and stable excitation wavelength of 488 nm rather than UV, it offered the possibility of ratiometric measurements on the basis of a real emission shift, and had superior resolution for the pH range 7-8. With SNARF-1 we found that keratinocytes cultured under low serum conditions (0.2%) contain a higher proportion of cells with relatively low intracellular pH compared to high serum cultures (6%). Furthermore, pH changes were followed by changes in relative DNA content. These findings suggest that intracellular pH can be an early functional proliferation marker for human keratinocytes.     

猫脑干上涎核节前神经元电活动的观察

在麻醉的32只猫记录了电刺激颌下腺神经支引起的上涎核平均场电位和单位放电。逆行电刺激颌下腺神经支引起的上涎核平均场电位分布在同侧脑干背面闩部头端5.5—8mm处,与过去的组织学结果大致符合。用微电极在上涎核记录了68个对刺激颌下腺神经支有反应的单位,其中33个单位作了碰撞试验。有9个单位符合逆向反应标准,它们是真正的颌下腺节前神经元,逆行反应的潜伏期为14.4±2.5ms,其轴突传导速度为2.9±0.1m/s。其他不符合逆向反应标准的单位,对刺激颌下腺神经支仍能发生反应,估计多为中间神经元。在一部分单位观察了电刺激舌神经或味觉刺激舌引起的反应。根据这些观察对上涎核内存在复杂神经元回路的可能性作了讨论。     

A mathematical model for the burden of diabetes and its complications

Background  

The incidence and prevalence of diabetes are increasing all over the world. Complications of diabetes constitute a burden for the individuals and the whole society.     

A two-dimensional mathematical model of percutaneous drug absorption

Background  

When a drug is applied on the skin surface, the concentration of the drug accumulated in the skin and the amount of the drug eliminated into the blood vessel depend on the value of a parameter, r. The values of r depend on the amount of diffusion and the normalized skin-capillary clearence. It is defined as the ratio of the steady-state drug concentration at the skin-capillary boundary to that at the skin-surface in one-dimensional models. The present paper studies the effect of the parameter values, when the region of contact of the skin with the drug, is a line segment on the skin surface.