Membrane depolarization induced by transcellular osmosis in internodal cells ofNitella flexilis

Summary Membrane depolarization induced by transcellular osmosis was studied using internodal cells ofNitella flexilis. Transcellular osmosis was induced by using sorbitol or methanol as the osmotic agent. In the endosmotic cell half, the membrane often generated an action potential and depolarized further with a concomitant decrease in membrane resistance. This osmosis-induced depolarization was a graded response dependent on the external osmotic gradients. However, in the exosmotic cell half, both membrane potential and membrane resistance changed insignificantly. Membrane depolarization occurred also in cells made inexcitable by bathing in 0.1–1 mM KCl solution.Effects of temperature and internal osmotic pressure on osmosis-induced depolarization were investigated. The magnitude of depolarization at low temperature (2 or 4°C) was larger than that at room temperature (around 20°C). Membrane depolarization was accelerated by lowering the internal osmotic pressure and inhibited by raising it.Not only the plasmalemma but the tonoplast also responded significantly to endosmosis.     

Ion movements induced by transcellular osmosis inNitella flexilis

Summary Movements of K⁺, Na⁺, and Cl^}- ions during transcellular osmosis were studied in internodal cells ofNitella flexilis. Much K⁺ was released from the endosmotic cell part, but only a little from the exosmotic cell part. The amount of K⁺ released depended on the osmotic gradient driving transcellular osmosis. Movement of Na⁺ was hardly detected. Cl^}- was released in nearly the same amounts as K⁺. Release of K⁺ from the endosmotic cell half was stimulated remarkably by lowering the temperature from 20 to 1 °C, and also by lowering the internal osmotic pressure but inhibited by raising it.The dependence of K⁺ release on osmotic gradient, internal osmotic pressure and temperature can be explained by their effects on membrane depolarization and membrane resistance (Hayama et al. 1978). We concluded thatP _K remained unchanged, whileP _Cl increased a great deal in the endosmotic cell part.     

An Improved Method for Identifying 8-O-Acetyl-N-Acetylneuraminic Acid

The periodic acid/thionin-Schiff/potassium hydroxide/periodic acid/fuchsin-Schiff sequence developed by Culling et al. frequently causes damage to sections and gives inconsistent results because of insufficient primary oxidation and difficulties in making the thionin-Schiff reagent. These disadvantages have been largely eliminated by more thorough primary oxidation and by replacing the original thionin-Schiff with a new cold thionin-Schiff. The effect of alkaline hydrolysis on thionin-aldehyde complexes was also studied and the reduction of color caused by this treatment was restored by a second thionin-Schiff reaction. The new sequence gives consistent results and imparts greater color to the thionin-Schiff reaction.     

Purification and Some Properties of Plant Serine Acetyltransferase

Serine acetyltransferase (SATase) that catalyzes the conversionof L-serine to O-acetyl-L-serine (OAS) in the presence of acetyl-CoAwas highly purified from rape leaf extract, using a coupledassay system in which OAS is converted to cysteine by enzymaticaction of exogenous cysteine synthase. Through purificationprocedures including heat treatment, ammonium sulfate fractionationand successive column chromatographies on DEAE-Toypearl, Blue-Toyopearland Toyopearl HW-55, the specific activity was raised to about4,800-fold over that in the crude extract. The molecular weightof rape enzyme was estimated to be about 350,000 by gel filtrationcolumn chromatography. The cysteine-forming activity of thefinal preparation was completely dependent on L-serine, acetyl-CoAand sulfide. However, this preparation had low activity forL-cysteine synthesis from L-serine even in the absence of exogenouscysteine synthase, suggesting that plant SATase exists as ahigh-molecular weight enzyme complexed with cysteine synthase. (Received November 6, 1987; Accepted March 25, 1988)     

Intraoperative gamma cameras for radioguided surgery: Technical characteristics,performance parameters,and clinical applications

Several small gamma cameras (SGCs) intended for surgical use are now in development or currently being marketed. In this review, we discuss the characteristics, performance, and clinical use of SGCs which are hand-held and small enough to be easily managed by surgeons during their procedures. We expect that SGCs have the potential to be used more widely in radioguided surgery. As advancing molecular imaging technologies will broaden clinical indications, SGCs will likely be used and integrated with other imaging modalities into numerous types of radioguided surgery in the near future.