Decreased membrane phospholipid packing and decreased cell size precede DNA cleavage in mature mouse B cell apoptosis.

Mature resting mouse spleen B cells progress stochastically into apoptosis at a uniform rate over the first 16 h in vitro in 3 stages. In stage 1, early apoptotic B cells decreased the normal phospholipid packing of their plasma membranes, detected as increased binding of the lipophilic dye merocyanine 540, and also decreased in volume, detected as decreased forward scatter. In stage 2 there was abrupt internucleosomal cleavage of DNA, quantitated as hypodiploid nuclei by flow cytometry. Some stage 2 cells entered stage 3, where the plasma membrane became permeable to propidium iodide. B cells in later stages of this sequence retained the characteristics of earlier stages, whereas nonapoptotic B cells remained in their original state. Cycloheximide increased the progression of B cells through these three stages, whereas dextran sulfate inhibited stage 1 more effectively than stages 2 or 3. Increased orthogonal scatter also occurred late in some of the cells that had passed through stage 1, but did not correlate well with propidium iodide permeability. Fresh small dense spleen B cells contained 5% to 7% stage 1 cells but only about 1% stage 2 cells. Macrophages have been reported to destroy preferentially apoptotic thymocytes by recognizing plasma membrane alterations deriving from loose packing of phospholipid head groups. The recognition of stage 1 rather than stage 2 B cells by macrophages may help to keep the proportion of apoptotic cells low in vivo.

Frequency response of long mass-spectrometer sampling catheters.

It was hypothesized that the long lengths of sampling catheters required when a mass spectrometer is multiplexed to more than one operating room limit the upper frequency at which a gas concentration may be determined accurately. This possibility has not been investigated. Known step changes of CO2 were generated by a solenoid valve driven by an electronic timer that was adjustable from 0.1 to 10 Hz. The valve alternated between 100% O2 and 7% CO2 in 50% O2 and balance N2. CO2 concentration was monitored by a mass spectrometer after the gas passed through a 3.7 m Teflon catheter or through 30 m Teflon, nylon, polyethylene (PE), or polyvinylchloride (PVC) catheters. Gas flow for all catheters was adjusted to 1.1 ml/s. The peak-to-peak output of the mass spectrometer was read from a storage oscilloscope. The 3.7 m catheter caused a 10% error at 5.5 Hz (330/min). In sharp contrast, 30 m catheters made from Teflon, PVC, and PE caused errors greater than 10% at only 0.6 Hz (36/min). The 30 m nylon catheter passed 1.1 Hz (66/min) with a 10% error. Teflon, PVC, and PE are not suitable materials from which to make long catheters sampling CO2. Because the frequency response of the nylon catheter appeared similar to that of a low-pass filter, an electronic circuit was designed and tuned to extend the high-frequency response of the catheter. With the circuit in place, the frequency at which a 10% error occurred in the measurement of CO2 improved from 1.1 Hz (66/min) to 2.2 Hz (132/min).(ABSTRACT TRUNCATED AT 250 WORDS)