Search

The transient receptor potential melastatin subfamily (TRPM), which is a mammalian homologue of cell death-regulated genes in Caenorhabditis elegans and Drosophila, has potential roles in the process of the cell cycle and regulation of [Ca.sup.2+] signaling. Among this subfamily, TRPM8 (also known as Trp-p8) is a [Ca.sup.2+]-permeable channel that was originally identified as a prostate-specific gene upregulated in tumors. Here we showed that the TRPM8 channel was expressed in human melanoma G-361 cells, and activation of the channel produced sustainable [Ca.sup.2+] influx. The application of menthol, an agonist for TRPM8 channel, elevated cytosolic [Ca.sup.2+] concentration in a concentration-dependent manner with an E[C.sub.50] value of 286 [micro]M in melanoma cells. Menthol-induced responses were significantly abolished by the removal of external [Ca.sup.2+]. Moreover, inward currents at a holding potential of -60 mV in melanoma cells were markedly potentiated by the addition of 300 [micro]M menthol. The most striking finding was that the viability of melanoma cells was dose-dependently depressed in the presence of menthol. These results reveal that a functional TRPM8 protein is expressed in human melanoma cells to involve the mechanism underlying tumor progression via the [Ca.sup.2+] handling pathway, providing us with a novel target of drug development for malignant melanoma. [Ca.sup.2+]-permeable channel; cell viability; G-361; malignant melanoma; menthol; transient receptor potential melastatin

Previous experiments have shown that an amino acid transport system [B.sup.0+] transporter in cultured colonic epithelial cells mediates amino acid absorption. Here we describe the cloning and functional characterization of a system [B.sup.0+] transporter selectively expressed in the colon. Using the combination of an expressed sequence tag database search and RT-PCR approaches, we cloned a mouse colonic amino acid transporter, designated [mCATB.sup.0+]. Northern blot analysis revealed that [mCATB.sup.0+] was selectively expressed in the large intestine. In situ hybridization showed the [mCATB.sup.0+] mRNA to be localized in absorptive epithelial cells. When expressed in Xenopus oocytes, [mCATB.sup.0+] exhibited a [Na.sup.+]-dependent stereoselective uptake and a broad specificity for neutral and cationic amino acids, which is characteristic of amino acid transport system [B.sup.0+]. In vivo [[sup.3]H]glycine uptake assay demonstrated that a system [B.sup.0+]-like transporter protein was expressed on the apical surface of the colonic absorptive cells. Our data suggest that a mouse colonic amino acid transporter [mCATB.sup.0+] may absorb amino acids from the intestinal contents in the colon. cDNA cloning; absorptive epithelial cell

Taste receptors located in taste-bud cells are activated leading to the ability to detect taste. A complementary DNA encoding a receptor for sour tastes has been identified. A rat circumvallate papilla cDNA library was constructed to isolate a sour-taste receptor. Clones were expressed in Xenopus laevis oocytes, and RNA transcripts from positive clones resulted in alteration of the extracellular pH to 5.5. Immunohistochemistry was used to determine the subcellular localization of mammalian degenerin-1 protein in the taste buds.