Studies on the outer surface of normal and RSV-transformed BHK fibroblast plasma membrane

Quantitation and topography of membrane proteins in highly water-permeable vesicles from ADH-stimulated toad bladder

Antidiuretic hormone (ADH) stimulation of toad bladder granular cells rapidly increases the osmotic water permeability (Pf) of their apical membranes by insertion of highly selective water channels. Before ADH stimulation, these water channels are stored in large cytoplasmic vesicles called aggrephores. ADH causes aggrephores to fuse with the apical membrane. Termination of ADH stimulation results in prompt endocytosis of water channel-containing membranes via retrieval of these specialized regions of apical membrane. Protein components of the ADH water channel contained within these retrieved vesicles would be expected to be integral membrane protein(s) that span the vesicle's lipid bilayer to create narrow aqueous channels. Our previous work has identified proteins of 55 (actually a 55/53-kDa doublet), 17, 15, and 7 kDa as candidate ADH water channel components. We now have investigated these candidate ADH water channel proteins in purified retrieved vesicles. These vesicles do not contain a functional proton pump as assayed by Western blots of purified vesicle protein probed with anti-H(+)-ATPase antisera. Approximately 60% of vesicle protein is accounted for by three protein bands of 55, 53, and 46 kDa. Smaller contributions to vesicle protein are made by the 17- and 15-kDa proteins. Triton X-114-partitioning analysis shows that the 55, 53, 46, and 17 kDa are integral membrane proteins. Vectorial labeling analysis with two membrane-impermeant reagents shows that the 55-, 53-, and 46-kDa protein species span the lipid bilayer of these vesicles. Thus the 55-, 53-, and 46-kDa proteins possess characteristics expected for ADH water channel components. These data show that the 55- and 53- and perhaps the 46-, 17-, and 15-kDa proteins are likely components of aqueous transmembrane pores that constitute ADH water channels contained within these vesicles.

Cell surface changes during muscle differentiation in vitro: a study with the probe 2,4,6-trinitrobenzene sulphonate

Cell surface changes during muscle differentiation in vitro, were investigated using the non permeant probe 2,4,6-trinitrobenzene sulphonate (TNBS) in order to label the aminogroups of proteins exposed on the outer surface of the plasma membrane. Surface proteins of chick myotubes and 'mature' unfused myoblasts (myoblasts grown for 7 days in a calcium-depleted medium) were found to bind an equal amount of probe, which is twice the amount bound by surface proteins in 'immature' myoblasts (1--2 days of culture) and fibroblasts. This indicates that a 'remodelling' of the plasma membrane outer surface takes place in the course of muscle cell differentiation even in the absence of cell fusion. Moreover, the total amount of TNBS bound to the surface was 4--5 times greater in myotubes than in unfused myoblasts. This appears to result from the surface expansion which occurs in myotubes during the development of the T tubule system.

Immunochemical purification of probe-labeled plasma membrane proteins: an approach to the molecular anatomy of the cell surface

The probe 2,4,6-trinitrobenzene sodium sulfonate may be used under appropriate conditions for selective labeling of plasma membrane proteins exposed at the outer cell surface. Labeled proteins, solubilized by detergents, can be purified by reverse immunoadsorption using antiprobe antibodies covalently linked to Sepharose 4B. This method has been applied to an investigation of the outer cell surface structure of chicken embryo and hamster fibroblasts. Coelectrophoresis in sodium dodecyl sulfate-polyacrylamide gels of probe-labeled membrane proteins purified from baby hamster kidney fibroblasts have shown that 7 major protein groups of different molecular weight are exposed on both control and Rous sarcoma or polyoma virus-transformed cells. Moreover, the transformed cells display a nonvirion component of 80--100 k daltons that is not labeled by the probe in normal cells. In fibroblasts transformed by a temperature sensitive Rous sarcoma virus mutant, that transforms at 37 degrees C but not at 41 degrees C, the expression of this component is related to the expression of the transformed phenotype.

The study of rous sarcoma virus-transformed baby hamster kidney cells using fluorescent probes

The fluorescent probes pyrene, pyrene butyric acid and N-phenyl 1-naphthylamine have been used to investigate the changes that accompany in vitro transformation of a baby hamster kidney cell line using Rous sarcoma virus. The fluorescent probes which reside in the membrane were used to compare the changes in microviscosity and polarity of the membranes of normal cells with two transformed cell lines. The spectrofluorimetric data indicate that following transformation the probe N-phenyl 1-naphthylamine resides in a more polar environment. However, using the probe pyrene, the yield of excimer indicates decreased mobility of this probe in the membrane of transformed cells. The data also indicate differences between the two transformed cell lines. Laser photolysis was used to study the lifetime of the pyrene probes and the quenching of the pyrene fluorescence in the membrane by several different quenching molecules. The data indicate differences between the three cell lines and suggest that transformation decreases movement within the membrane.