Agonist-activated cobalt uptake identifies divalent cation-permeable kainate receptors on neurons and glial cells.

Activation of kainate receptors causes Co2+ influx into neurons, type-2 astrocytes, and O-2A progenitor cells. Agonist-activated Co2+ uptake can be performed using cultured cells or fresh tissue slices. Based on the pattern of response to kainate, glutamate, and quisqualate, three functionally different kainate-activated ion channels (K1, K2, and K3) can be discriminated. Co2+ uptake through the K1 receptor was only activated by kainate. Both kainate and glutamate activated Co2+ uptake through the K2 receptor. Co2+ uptake through the K3 receptor was activated by all three ligands: kainate, glutamate, and quisqualate. Co2+ uptake occurred through a nonselective cation entry pathway permeable to Co2+, Ca2+, and Mn2+. The agonist-dependent activation of divalent cation influx through different kainate receptors could be correlated with expression of certain kainate receptor subunit combinations. These results are indicative of kainate receptors that may contribute to excitatory amino acid-mediated neurotoxicity.

Xanthines with C8 chiral substituents as potent and selective adenosine A1 antagonists.

Several 8-substituted 1,3-dipropylxanthines were synthesized, and their receptor binding affinities at adenosine A1 and A2 receptors were measured. When enantiomeric pairs of compounds were examined, the R enantiomers were significantly more potent than the corresponding S enantiomers. The most potent compound at the A1 receptor was (R)-3,7-dihydro-8-(1-methyl-2-phenylethyl)-1,3-dipropyl-1H-purine-2,6-di one (5a; MDL 102,503), whose Ki value at the A1 receptor was 6.9 nM. However, a more selective compound was (R)-3,7-dihydro-8-(1-phenylpropyl)-1,3-dipropyl-1H-purine-2,6-dione (5d; MDL 102,234), which had a Ki value of 23.2 nM at the A1 receptor and an A2/A1 ratio of 153.

Demonstration of a second pharmacologically active promoter region in the NGF gene that induces transcription at exon 3.

Nerve growth factor (NGF) has been demonstrated to facilitate neurite outgrowth, rescue neurons from injury, and prevent programmed cell death in neurons. However, the therapeutic potential of NGF is limited by metabolic instability and poor CNS penetration. These limitations might be circumvented by identifying compounds which increase endogenous production of NGF in the brain. We sought to determine the site of all pharmacologically inducible promoters in the NGF gene using a differential analysis based on semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Mouse L929 cells were serum deprived and NGF mRNA was induced by treatment with phorbol 12-myristate 13-acetate (PMA), 1,25-dihydroxy-vitamin D3 (calcitriol) or horse serum. An increase in transcripts initiating at exon 1 was noted in cDNA from cells induced with all three agents. In addition, we also observed an increase in cDNA transcripts that initiate at exon 3 and do not include exons 1 and 2 (4.38 +/- 0.42, 2.56 +/- 0.05 and 3.04 +/- 0.03 fold increase over control for PMA, calcitriol and serum, respectively). Each of these increases was completely inhibited in the presence of actinomycin D, indicating that the increased levels of mRNA were due to increases in transcription and not mRNA stabilization. These results confirm the previous demonstration of a promoter for NGF near exon 1 and establish a pharmacologically inducible promoter in the NGF gene near exon 3 that could be targeted for therapeutic intervention.

Isolation and cDNA sequence of human postheparin plasma hepatic triglyceride lipase.

Hepatic triglyceride lipase (H-TGL) was isolated from human postheparin plasma by column chromatography on heparin-Sepharose and phenyl-Sepharose and immunoaffinity chromatography with monoclonal antibodies. The purified enzyme had an apparent molecular weight of 65,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an amino-terminal sequence of Leu-Gly-Gln-Ser-Leu-Lys-Pro-Glu. Partial amino acid sequences of seven cyanogen bromide peptides were obtained. A human hepatoma cDNA library was screened with synthetic oligonucleotides derived from the partial protein sequence. The cloned H-TGL cDNA of 1569 nucleotides predicts a mature protein of 477 amino acids plus a leader sequence of 22 amino acids. Blot hybridization analysis of poly(A)+ mRNA with a putative H-TGL cDNA clone gave a single hybridizing band of 1.7 kilobases. The protein contains four consensus N-glycosylation sequences based on the cDNA sequence. Comparison of the enzyme sequence with that of other lipases reveals highly conserved sequences in regions of putative lipid and heparin binding. The carboxyl terminus of H-TGL contains a highly basic sequence which is not reported to be present in rat H-TGL or other members of the lipase gene family.