Worcester Foundation for Biomedical Research

About: Worcester Foundation for Biomedical Research is a based out in . It is known for research contribution in the topics: Estrone & Estrogen. The organization has 2195 authors who have published 2646 publications receiving 115809 citations. The organization is also known as: Worcester Foundation for Experimental Biology.

Tetrandrine blocks a slow, large-conductance, Ca2+-activated potassium channel besides inhibiting a non-inactivating Ca2+ current in isolated nerve terminals of the rat neurohypophysis

Abstract: The effects of tetrandrine, a bis-benzyl-isoquinoline alkaloid, on voltage-gated Ca2+ currents (I Ca) and on Ca2+-activated K+ current (I K(Ca)) and channels in isolated nerve terminals of the rat neurohypophysis were investigated using patch-clamp techniques. The non-inactivating component of I Ca was inhibited by external tetrandrine in a voltage- and dose-dependent manner, with an IC50=10.1 μM. I K(Ca) was elicited by depolarizations when approximately 10 μM Ca2+ was present on the cytoplasmic side. Only externally applied tetrandrine, at 1 μM, decreased the amplitude of I K(Ca), whereas the fast inward Na+ current and transient outward K+ current were not affected. Tetrandrine, applied to the extracellular side of outside-out patches excised from the nerve terminals, induced frequent and short closures of single type II, maxi-Ca2+-activated K+channels. Tetrandrine decreased the channel-open probability, within bursts, with an IC50=0.21 μM. Kinetic analysis of the channel activity showed that the open-time constant decreased linearly with increasing tetrandrine concentrations (0.01–3 μM), giving an association rate constant of 8.8×108 M−1s−1, whereas the arithmetic mean closed time did not change, giving a dissociation rate constant of 136.6s−1. These results show that tetrandrine is a high-affinity blocker of the type II, maxi-Ca2+-activated K+ channel of the rat neurohypophysial terminals.

Methylation of atypical protein aspartyl residues during the stress response of HeLa cells.

Abstract: A protein carboxyl methyltransferase (PCMT), which specifically modifies atypical protein L-isoaspartyl and D-aspartyl residues, is widely distributed in eucaryotic cells, but the factors that regulate its activity in vivo have not been identified. It has been proposed that the PCMT initiates the repair of structurally damaged proteins. To test the possibility that the concentration of structurally abnormal cellular proteins affects PCMT activity, protein carboxyl methylation reactions were studied in HeLa cells exposed to various stresses that increase the extent of protein unfolding in cells. Protein carboxyl methylation rates increased 70-80% during incubations at 42 degrees C and remained elevated for periods of up to 8 hr. This sustained increase was greater than that predicted from thermal effects on the enzyme alone and may reflect the exposure of atypical aspartyl sites as proteins unfold as well as increased rates of protein deamidation and isomerization at elevated temperatures. Methylation rates showed no increases following 12 hr incubations with the amino acid analogs L-azetidine-2-carboxylic acid or L-canavanine. Northern blot analysis of RNA preparations from control and stressed cells revealed three major transcripts for the PCMT in HeLa cells, which are 1.6, 2.6, and 4.5 kb in length. The concentrations of all three transcripts decreased by approximately 20% from control levels during heat shock. No changes in PCMT transcript concentrations were observed during incubation with the amino acid analogs. By contrast, large increases in the concentrations of hsp70 and ubiquitin transcripts were observed following either heat or chemical stresses. The results demonstrate that the PCMT is a constitutive component of cells whose function is required under normal conditions as well as during stress conditions, which accelerate structural damage to cellular proteins.

Triggered pore-forming agents

Abstract: An inactive pore-forming agent which is activated to lytic function by a condition such as pH, light, heat, reducing potential, or metal ion concentration, or substance such as a protease, at the surface of a cell.