Common genetic variation near the connexin-43 gene is associated with resting heart rate in African Americans: a genome-wide association study of 13,372 participants.

BACKGROUND: Genome-wide association studies have identified several genetic loci associated with variation in resting heart rate in European and Asian populations. No study has evaluated genetic variants associated with heart rate in African Americans. OBJECTIVE: To identify novel genetic variants associated with resting heart rate in African Americans. METHODS: Ten cohort studies participating in the Candidate-gene Association Resource and Continental Origins and Genetic Epidemiology Network consortia performed genome-wide genotyping of single nucleotide polymorphisms (SNPs) and imputed 2,954,965 SNPs using HapMap YRI and CEU panels in 13,372 participants of African ancestry. Each study measured the RR interval (ms) from 10-second resting 12-lead electrocardiograms and estimated RR-SNP associations using covariate-adjusted linear regression. Random-effects meta-analysis was used to combine cohort-specific measures of association and identify genome-wide significant loci (P≤2.5×10(-8)). RESULTS: Fourteen SNPs on chromosome 6q22 exceeded the genome-wide significance threshold. The most significant association was for rs9320841 (+13 ms per minor allele; P = 4.98×10(-15)). This SNP was approximately 350 kb downstream of GJA1, a locus previously identified as harboring SNPs associated with heart rate in Europeans. Adjustment for rs9320841 also attenuated the association between the remaining 13 SNPs in this region and heart rate. In addition, SNPs in MYH6, which have been identified in European genome-wide association study, were associated with similar changes in the resting heart rate as this population of African Americans. CONCLUSIONS: An intergenic region downstream of GJA1 (the gene encoding connexin 43, the major protein of the human myocardial gap junction) and an intragenic region within MYH6 are associated with variation in resting heart rate in African Americans as well as in populations of European and Asian origin.

Binding of terbium and cisplatin to C13* human ovarian cancer cells using time-resolved terbium luminescence.

Terbium (Tb3+) has been shown to increase the cellular accumulation and cytotoxicity of cisplatin in cisplatin-resistant human breast and ovarian cancer cells. Time-resolved Tb3+ luminescence was used to describe the binding of cisplatin to cisplatin-resistant C13* cells. A high-affinity Tb3+ binding site was identified in the plasma membrane of the C13* cells (n=105+/-2 fmol/cell and Kd=36. 3+/-5.2 microM). The binding of Tb3+ is suggested to occur through a cation-pi interaction with tryptophan residues in the plasma membrane, resulting in an enhancement of the intensity and lifetime of Tb3+. Stern-Volmer quenching analysis revealed that the Tb3+ binding site is not readily accessible to the aqueous environment. The quenching of the Tb3+-C13* intensity by cisplatin occurred by static quenching processes, involving both a direct electron-exchange interaction as well as an indirect dipole-dipole resonant energy transfer mechanism. Formation of the Tb3+-C13*-cisplatin complex does not interfere with the high-affinity binding of Tb3+; cisplatin and Tb3+ bind within 5 to 10 A of each other. A specific terbium/cisplatin binding protein is suggested to play a role in the cellular accumulation and cytotoxicity of cisplatin. Therefore, the transport of cisplatin across the plasma membrane must also involve a facilitated diffusion process. Our results indicate that the binding of Tb3+ to the plasma membrane may be potentially useful in the reversal of cisplatin resistance.

Effects of terbium on the cytotoxicity of cisplatin in FaDu human head and neck squamous cell carcinoma.

In this investigation, we report a relationship between the terbium (Tb3+) binding protein and the cytotoxicity of cisplatin in human head and neck cancer cells. In the FaDu cell line, the cytotoxic action of cisplatin was shown to be approximately six times more potent than the cytotoxicity of Tb3+. When cisplatin was combined with 80 microM Tb3+, the IC20 and IC50 values for cisplatin were reduced by 70% and 24%, respectively. The IC80 value, however, was increased by 124%. The results suggest that the cytotoxicity of cisplatin is enhanced by Tb3+ at low cisplatin concentrations. In agreement with previous studies, calcium and cisplatin were found to be mixed-type and noncompetitive inhibitors, respectively, of the Tb3+ -FaDu intensity. These findings imply that the receptor binding of Tb3+ can modulate the cytotoxic activity of cisplatin.