Increased DNA content of HSR-marker chromosomes of human neuroblastoma cells

Scanning cytophotometry demonstrates that the DNA content of human neuroblastoma chromosomes containing a specific abnormal segment—the Homogeneously Staining Region (HSR)—is significantly greater than that of homologous normal chromosomes without this segment. The potential significance of this finding and its relationship to another chromosome abnormality, the double minutes, is discussed.     

Regulation of Membrane Transport Sites for Amino Acids in Myogenic Cells

Abstract. Myoblasts from 12-day chick embryos in cell culture transport the nonmetabolizable amino acid α-aminoisobutyric acid (AIB) two to three-fold more rapidly than multinucleated myotubes which form from them. This decrease in transport is due to a relative decrease in the number of transport sites per unit area of cell surface suggesting a compositional change in the plasma membrane during myogenesis. In studies reported here, AIB transport was monitored throughout myogenesis and correlated with other aspects of differentiation. During myogenesis the number of amino acid transport sites remains constant per myotube nucleus. As myogenesis proceeds, there is a marked increase in cellular protein and cell surface without a commensurate increase in amino acid transport sites. The net consequence of the surface area change is fewer amino acid transport sites per unit area of myotube membrane surface. The decrease in membrane transport sites for AIB per unit area of membrane is not a result of length of time in culture per se, medium depletion, or cell density, but is a result of differentiation, since blocking myoblast fusion by deprivation of calcium delays the decrease in AIB transport sites per unit cell surface area while reversal of the calcium deprivation block is accompanied by a rapid decrease in the number of AIB transport sites per unit cell surface area. Thus, the decrease in AIB transport sites is an aspect of differentiation which accompanies the marked elaboration of surface membrane during myogenesis.     

Regulation of membrane transport sites for amino acids in myogenic cells. A differentiation dependent phenomenon

Myoblasts from 12-day chick embryos in cell culture transport the nonmetabolizable amino acid alpha-aminoisobutyric acid (AIB) two to three-fold more rapidly than multinucleated myotubes which form from them. This decrease in transport is due to a relative decrease in the number of transport sites per unit area of cell surface suggesting a compositional change in the plasma membrane during myogenesis. In studies reported here, AIB transport was monitored throughout myogenesis and correlated with other aspects of differentiation. During myogenesis the number of amino acid transport sites remains constant per myotube nucleus. As myogenesis proceeds, there is a marked increase in cellular protein and cell surface without a commensurate increase in amino acid transport sites. The net consequence of the surface area change is fewer amino acid transport sites per unit area of myotube membrane surface. The decrease in membrane transport sites for AIB per unit area of membrane is not a result of length of time in culture per se, medium depletion, or cell density, but is a result of differentiation, since blocking myoblast fusion by deprivation of calcium delays the decrease in AIB transport sites per unit cell surface area while reversal of the calcium deprivation block is accompanied by a rapid decrease in the number of AIB transport sites per unit cell surface area. Thus, the decrease in AIB transport sites is an aspect of differentiation which accompanies the marked elaboration of surface membrane during myogenesis.     

Occurrence of norspermine in Euglena gracilis.

A series of fluorescent probes which locate a graded series of depths from the surface to the centre of the lipid bilayer have been used to measure the fluidity gradient in liposomes and natural membranes. In dioleoyl phosphatidylcholine liposomes and in cells which have a high content of unsaturated phospholipids, a region of high microviscosity is detected near the cis double bond/s. The significance of this phenomenon is discussed in terms of the penetration and lateral movement of membrane protein.