Dynamics of intracellular pH during apoptotic and necrotic death of lymphocytes was studied with the help of fluorescent pH-sensitive probe BCECF. Change in intracellular pH is an early differential marker of apoptotic and necrotic types of death in thymus lymphocytes.

The use of potential-sensitive fluorescent probes allowed us to estimate transmembrane potentials of the plasma (Ad~.) and mitochondrial (Adpm) membranes of rat thymocytes, which were -58_+3 mV and -169-+'~ mV, respectively. Dexamethasone-induced apoptosis led to a significant decrease in Adpp (by 55%) and Adam (by 17%). This effects of dexamethasone was dose-and time-dependent. Changes in AdPm were greater and preceded those in Aqbp. Key Words: apoptosis; transmembrane potential; glucocorticoids; thymocytesApoptosis is a type of autoregulation directed to the removal of "excess" biological material. During the embryonal development this mechanism is triggered in dividing autoreactive T-cell clones in the thymus, aging neutrophils, prostatic and endometrial ceils (which are not affected by tropic sex steroid hormones), and populations of intensely proliferating cells in the absence of growth factors in the medium (spontaneous apoptosis) [6,7].Recent studies have revealed specific features of apoptosis. Morphological changes include condensation of the cytoplasm and chromatin, cells fragmentation, and formation of apoptotic bodies. A decrease in the cell volume 2-3 h after the addition of inducing agent is the earliest morphological manifestation of apoptosis [8]. We have developed a rapid method for the recording and analysis of changes in the volume of thymocytes. This method is based on an analog-todigital conversion of results in a MacLab/2e system with subsequent computer data processing. We showed that dexamethasone-induced apoptosis decreases the volume of lymphocytes by 7-29%. This decrease depends on the preparation concentration and incubation time [3].A decrease in the volume of lymphocytes in apoptosis is associated with change in the ion flux through the cell membrane [9,10]. The data suggest that apo- The method of potential-sensitive tluorescent probes (PFP) is used for a quantitative analysis of the TMP of cells [1,2]. The possibility for simultaneous registration of potentials of the plasma and mitochondrial membranes, insignificant effects of probes (in the working concentration range) on cell respiration and viability, and the absence of plasma membrane damages observed during a microelectrode assay are the advantages of the PFP method. The distribution of PFPs in cells and mitochondria can be analyzed by registering their fluorescence. PFPs are accumulated in cells and mitochondria by the gradient of their TMPs. The fluorescence of probes changes differently. Fluorescence intensity (FI) of many amphiphilic cationic probes increases with an increase in potentials. On the contrary, FI of cyanic and merocyanic stains and anionic probes (ANS and oxolon stains) decreases with an increase in potentials. TMPs of various cells were intensely studied by using PFPs [7,12,14]. Values of Aqb of the mitochondrial and plasma membranes in lymphocytes, macrophages, hepatocytes, and adipocytes were determined. However, changes of the TMP in apoptosis are less investigated.Here we studied the TMP of rat thymocyt...