Multielement determination and speciation of major-to-trace elements in black tea leaves by ICP-AES and ICP-MS with the aid of size exclusion chromatography.

A multielement determination of major-to-trace elements in black tea leaves and their tea infusions was carried out by ICP-AES (inductively coupled plasma atomic emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry). Tea infusions were prepared as usual tea beverage by brewing black tea leaves in boiling water for 5 min. About 40 elements in tea leaves and tea infusions could be determined over the wide concentration range in 8 orders of magnitude. The extraction efficiency of each element was estimated as the ratio of its concentration in tea infusions to that in tea leaves. From the experimental results for the extraction efficiencies, the elements in black tea leaves were classified into three characteristic groups: (i) highly-extractable elements (>55%): Na, K, Co, Ni, Rb, Cs and Tl, (ii) moderately-extractable elements (20-55%): Mg, Al, P, Mn and Zn, and (iii) poorly-extractable elements (<20%): Ca, Fe, Cu, Sr, Y, Zr, Mo, Sn, Ba and lanthanoid elements. Furthermore, speciation of major-to-trace elements in tea infusions was performed by using a combined system of size exclusion chromatography (SEC) and ICP-MS (or ICP-AES). As a result, many diverse elements were found to be present as complexes associated with large organic molecules in tea infusions.

Molecular cloning and the functional expression of two isoforms of human metabotropic glutamate receptor subtype 5.

We previously reported that a variant with extra amino acids exists in rat metabotropic glutamate receptor subtype 5 (mGluR5) and that the identical extra sequence also exists in the human mGluR5 cDNA. We herein report the complete sequence and the functional expression of two isoforms of mGluR5 from the human brain. The deduced amino acid sequence of the large extracellular domain is extremely well conserved between rat and human mGluR5 (98.6%) which suggests that the amino-terminal region of mGluR5 is functionally important. We show that the glutamate-evoked responses appear in Xenopus oocytes while expressing either of the two mGluR5 isoforms, which suggests that these two receptors from the human brain could activate phospholipase C and generate Ca(2+)-activated Cl- current. We compared some of the pharmacological profiles of these two isoforms, but no clear differences could be observed. Finally, we also examined the effect of exogenous G proteins on the mGluR5-evoked responses.

A variant of metabotropic glutamate receptor subtype 5: an evolutionally conserved insertion with no termination codon.

We herein report the presence of a variant of the rat metabotropic glutamate receptor subtype 5 (mGluR5) cDNA. In this variant, named mGluR5b, an extra 96 bp sequence is inserted into the originally reported mGluR5 cDNA. The position of this insertion corresponds to that of the 85 bp insertion reported for the alternative form of mGluR1, another subtype of the receptors (designated as mGluR1 beta). No sequence-similarity was found between the additional sequences of the mGluR1 beta and the mGluR5b. While the additional sequence of the mGluR1 beta cDNA contains a translation termination codon in the frame, that of the mGluR5b cDNA does not. This identical 96 bp insertion was also found in a human mGluR5 cDNA clone. Northern blot analyses with the mGluR5b-specific probe showed that the expression of mRNA for this species is regulated in a region-specific manner in the rat brain.