Ultrastructural aspects of colchicine ultrasensitivity in CLL lymphocytes

Circulating lymphocytes from patients with chronic lymphatic leukaemia show extreme sensitivity to colchicine, with 80%-90% cell death after exposure to 10(-7) M colchicine for 20 h in vitro. This is 100,000-times greater than the dose required (10(-2) M) for a similarly toxic effect on normal lymphocytes. A time course series of fixations during the 20-h exposure of chronic lymphoid leukaemia (CLL) lymphocytes to 10(-7) colchicine revealed an entire spectrum of ultrastructural alterations well in advance of any sign of cell death, previously only ascertained by nuclear pycnosis in the light microscope. The changes included the appearance of large numbers of intermediate filaments, loss of surface microvilli, mitochondrial alterations and the formation of annulate lamellae. Mitochondrial changes included disruption of the cristae, swelling and tight clumping of the entire mitochondrial population into a single region of the cytoplasm.     

Cation induced changes in the rheological properties of purified mucus glycoprotein gels

The effects of mono-, di- and trivalent ions on the rheological properties of a purified mucus glycoprotein gel have been investigated. Monovalent ions increased the fluidity of the gels in a concentration dependent manner. The effect of calcium was pH dependent; at neutral pH values this ion produced a maximum in the gel viscoelasticity at a concentration of 0.5 mM, whilst at pH 5.0 the increase in viscoelasticity was sustained up to 3.0 mM. The same concentrations of copper (II) at pH 5.0 had a similar but greater effect on the viscoelasticity. Al3+ at pH 3.0 increased the viscoelastic moduli throughout the range studied (0.1-2.0 mM), whereas iron made the gels more fluid at low concentrations, but increased the viscoelasticity to above control values at a concentration of 2.0 mM.     

Differentiation of tropomyosin-containing myofibrils in cleavage-arrested ascidian zygotes expressing acetylcholinesterase

Two muscle differentiation programs, acetylcholinesterase and tropomyosin-containing filaments and fibrils, occur together in the same cleavage-arrested zygotes (1-celled) of the ascidian Ciona intestinalis. Coexpression in such undivided but developing 'embryos' is consistent with the idea that separate elements of muscle differentiation are related at some regulatory level, perhaps through a single multi-gene regulatory factor. Fertilized Ciona eggs were exposed to cytochalasin B for 20 h and then briefly reacted histochemically for acetylcholinesterase activity. Strongly reacting specimens were selected and processed for transmission electron microscopy to reveal regions of muscle ultrastructure. Every acetylcholinesterase-reactive zygote tested contained muscle contractile elements; no example lacking acetylcholinesterase was found with myofilaments and myofibrils. As demonstrated by immunogold labelling, a polyclonal antibody to tropomyosin from Ciona adult body wall reacted differentially with the presumed ultrastructural muscle elements in cleavage-arrested zygotes. Site-specific reactions were also observed in larval tail muscle and the siphon muscles of postmetamorphic zooids.