Faculty Bibliography

Human endothelin (ET) A receptor (hETAR) is a G-protein-mediated receptor that binds ET1 with high affinity and ET2 and ET3 with lower affinities. ET1 is the most potent endogenous vasoconstrictor known at this time. When expressed in Xenopus laevis oocytes, hETAR is rapidly desensitized after stimulation with ET1. This desensitization lasts 90-110 min. Human neurokinin A (hNKAR) and human serotonin type 2 receptors were also expressed in the Xenopus system for comparison to hETAR. hNKAR desensitizes for 25-35 min, while the serotonin receptor does not appear to desensitize. To examine the role of the cytoplasmic tail of hETAR in desensitization, deletion mutations were constructed which remove 11, 36, and 51 amino acids from the cytoplasmic tail. The mutations removing 11 and 36 residues were functional, but the mutation removing 51 amino acids was not functional. The two functional mutations have a resensitization time similar to that of hETAR. In summary, the prolonged desensitization time of hETAR is unique for G-protein-mediated receptors and may attenuate the adverse physiological effects of the endothelin family. In addition, the cytoplasmic tail of hETAR does not appear to play a role in desensitization or resensitization of this receptor

Four related genes, Shaker, Shab, Shaw, and Shal, encode voltage-gated K+ channels in Drosophila. Multigene subfamilies corresponding to each of these Drosophila genes have been identified in rodents and primates; this suggests that the four genes are older than the common ancestor of present-day insects and mammals and that the expansion of each into a family occurred before the divergence of rodents and primates. In order to define these evolutionary relationships more precisely and to facilitate the search for mammalian candidate K+ channel gene mutations, we have mapped members of the Shaw-homologous gene family in humans and mice. Fluorescence in situ hybridization analysis of human metaphase chromosomes mapped KCNC2 (KShIIIA, KV3.2) and KCNC3 (KShIIID, KV3.3) to Chromosome (Chr) 19q13.3-q13.4. Inheritance patterns of DNA restriction fragment length variants in recombinant inbred strains of mice placed the homologous mouse genes on distal Chr 10 near Ms15-8 and Mdm-1. The mouse Kcnc1 (KShIIIB, NGK2-KV4, KV3.1) gene mapped to Chr7 near Tam-1. These results are consistent with the hypothesis that the generation of the mammalian KCNC gene family included both duplication events to generate family members in tandem arrays (KCNC2, KCNC3) and dispersion of family members to unlinked chromosomal sites (KCNC1). The KNCN2 and KCNC3 genes define a new synteny group between humans and mice

Several genes (the Shaker or Sh gene family) encoding components of voltage-gated K+ channels have been identified in various species. Based on sequence similarities Sh genes are classified into four groups or subfamilies. Mammalian genes of each one of these subfamilies also show high levels of sequence similarity to one of four related Drosophila genes: Shaker, Shab, Shaw, and Shal. Here we report the isolation of human cDNAs for a Shaw-related product (NGK2, KV3.1a) previously identified in rat and mice. A comparison of the nucleotide and deduced amino acid sequence of NGK2 in rodents and humans shows that this product is highly conserved in mammals; the human NGK2 protein shows over 99% amino acid sequence identity to its rodent homologue. The gene (NGK2-KV4; KCNC1) encoding NGK2 was mapped to human chromosome 11p15 by fluorescence in situ hybridization with the human NGK2 cDNAs