Arg389Gly polymorphism of the human beta1-adrenergic receptor in patients with nonfatal acute myocardial infarction.

BACKGROUND: We sought to investigate the relation between the Arg389Gly polymorphism in the human beta1-adrenergic receptor (ADRB1) gene and acute myocardial infarction (AMI). It was previously reported that augmented sympathetic activity might play an important role as a trigger of AMI by enhanced hemodynamic or mechanical forces through ADRB1 activation. Recently, a common polymorphism has been identified at amino acid position 389 (Arg or Gly) of the human ADRB1, within a region important for receptor-Gs protein coupling and subsequent agonist-stimulated adenylyl cyclase activation. METHODS: To investigate the relation between the Arg389Gly polymorphism in the ADRB1 gene and AMI, we genotyped 354 patients with AMI and 354 age- and sex-matched control subjects by use of polymerase chain reaction amplification and the restriction fragment length polymorphism analysis. RESULTS: The prevalence of the Arg389 homozygote (CC) genotype was significantly more frequent in patients with AMI than in control subjects (68.1% vs 47.2%, P <.0001). In logistic regression models, the odds ratio (OR) of Arg389 homozygote (CC) versus Arg389Gly heterozygote (CG) + Gly389 homozygote (GG) genotypes between control subjects and patients with AMI was 2.86 (95% CI 1.92-4.26, P =.0001). The association of the Arg389Gly polymorphism of ADRB1 with AMI was statistically significant and independent of other risk factors. CONCLUSION: Our findings suggest that the genotype of Arg389Gly polymorphism in the human ADRB1 gene is associated with AMI.

Circulating T-lymphocyte activation in patients with variant angina.

BACKGROUND: Both experimental and pathological studies suggest that immune response and inflammation may play an important role in the pathogenesis of coronary spasm. DESIGN: To elucidate the role of systemic immune and inflammatory responses in the pathogenesis of coronary spasm, we studied circulating T-lymphocyte activation in variant angina patients (VAPs), stable effort angina patients (EAPs) and in control participants. METHODS: Twenty documented VAPs, 13 EAPs and 20 control participants were studied. To evaluate T-lymphocyte activation, T-lymphocyte surface antigen expression, including CD3, CD4, CD8 and HLA-DR, was measured by two-colour flow cytometric analysis. Serum-soluble interleukin-2 receptor (sIL-2R) and C-reactive protein (CRP) were also measured by enzyme-linked immunosorbent assay. We restudied 10 of the VAPs to investigate the relationship between the disease activity of variant angina and T-lymphocyte activation. RESULTS: The percentage of CD3+/DR+ T-lymphocytes in VAPs (14.8%) was significantly higher than in EAPs (10.7%, P < 0.05) and control participants (9.7%, P < 0.005); however, levels of sIL-2R were the same among the three groups. Levels of CRP were within normal range in all VAPs. The percentage of CD8+/DR+ T-lymphocytes was significantly higher in VAPs (9.5%, P < 0.005) than in EAPs (5.5%) and control participants (5.9%), whereas the percentage of CD4+/DR+ T-lymphocytes was similar among the three groups. The percentage of activated T-lymphocytes in VAPs was unchanged during the follow-up period (mean intervals, 10 months). CONCLUSIONS: These results indicate that the chronic activation of T-lymphocytes, especially CD8+ T-lymphocytes, may be involved in the pathogenesis of coronary spasm.

N-Ethylmaleimide Stimulates and Inhibits Ion Transport in Vestibular Dark Cells of Gerbil.

Vestibular dark cell epithelium was isolated from the semicircular canal of gerbils to test the proposal that the sulfhydryl alkylating agent N-ethylmaleimide (NEM) inhibits K(+) secretion by this tissue and does so by reacting with a site in or near the apical membrane. Dark cell epithelium was mounted in a micro-Ussing chamber for measurements of transepithelial voltage (V(t)) and resistance (R(t)) or in a perfused bath on the stage of a microscope for measurement of cell height as an index of cell volume. Perfusion of the apical or basolateral side with 10(-3) M NEM caused an increase in V(t) superimposed upon a slower decrease of V(t), resulting in a triphasic response. There were only small changes in R(t). Under this condition, V(t) is proportional to short circuit current and to K(+) secretion. Both the stimulatory and the inhibitory responses of V(t) were dose-dependent between 10(-6) and 10(-3) M NEM and the inhibition was irreversible. The specificity of the reaction of NEM with sulfhydryl groups was confirmed by the use of the reducing agent dithiothreitol (DTT). Perfusion of 5×10(-4) M DTT on the apical side caused no significant changes in V(t) but completely prevented both stimulation and inhibition of V(t) by NEM (10(-3) M). The amplitudes of the stimulation and the inhibition of V(t) were greater for basolateral than for apical perfusion of NEM. Similarly, the response times for each effect were faster from the basolateral side, suggesting that the primary sites of action are at or near the basolateral membrane. The site of action of NEM was further explored by subjecting the tissue to a membrane-impermeant sulfhydryl reagent, stilbenedisulfonate maleimide (SDM). Apical perfusion of 10(-3) M SDM had no effect on V(t) or R(t), whereas basolateral perfusion caused a reversible increase of V(t) (5.2 ± 0.5 to initially 6.8 ± 0.5 mV which relaxed after 60 s to 5.8 ± 0.5 mV) and to an initial decrease in R(t) by 4%. No inhibitory phase was observed. Elevation of basolateral [K(+)] from 3.6 to 25 mM is known to increase V(t) and reduce R(t) via direct stimulation of basolateral K(+) uptake and indirect stimulation of the apical membrane conductance. Basolateral perfusion of 10(-3) M NEM fully inhibited the increase of V(t) due to 25 mM K(+). Elevation of basolateral [K(+)] from 3.6 to 25 mM is known to increase reversibly cell volume. NEM was found to inhibit cell swelling in a dose-dependent manner but did not initially affect the rate of shrinking after K(+)-induced swelling, pointing to action only on basolateral transport pathways. The effects of NEM on K(+)-induced cell swelling were completely prevented by 5×10(-4) M DTT, demonstrating that the inhibitory effect of NEM was on sulfhydryl groups. In contrast to interpretations of NEM action in frog semicircular canal, we have found that NEM appears to stimulate an ion transport process in mammalian dark cells at an extracellular site in the basolateral membrane and inhibits another ion transport process in the basolateral membrane at another site. Inhibition by NEM from the apical side occurs most likely by diffusion of the agent to a site at or near the cytosolic side of the basolateral membrane.

Suppressive effect of the Gly389 allele of the beta1-adrenergic receptor gene on the occurrence of ventricular tachycardia in dilated cardiomyopathy.

Beta-1-adrenergic receptor (beta1-AR) blockers reduce both the incidence of sudden death and the ventricular volume in heart failure. In vitro, the Gly389 variant of beta1-AR mediates less adenylyl cyclase activities than the Arg389 variant, so Arg389Gly polymorphism was investigated with regard to the genesis, progression, or arrhythmogenesis of dilated cardiomyopathy (DCM). Allele and genotype frequencies of the Arg389Gly polymorphism were determined in 163 DCM patients and 157 age- and sex-matched controls. There were no differences in genotype and allele frequencies between patients and controls. Echocardiograms, left ventriculograms and 24h-Holter electrocardiograms were evaluated in the DCM patients and none of the clinical indices, other than ventricular tachycardia (VT), differed among the 3 genotypes. The Gly389 allele was more frequent in the VT(-) group than in the VT(+) group (0.46 vs 0.24, p=0.001). In univariate analysis, the odds ratio for VT in patients carrying 1 or 2 copies of the Gly389 allele was 0.29 ([95% confidence interval, 0.13-0.64], p=0.002), when compared with the Arg389 homozygotes. The Gly389 variant supressed the occurrence of VT in DCM, suggesting that this allele confers a decreased risk of sudden death.

The cardiac mechanical stretch sensor machinery involves a Z disc complex that is defective in a subset of human dilated cardiomyopathy.

Muscle cells respond to mechanical stretch stimuli by triggering downstream signals for myocyte growth and survival. The molecular components of the muscle stretch sensor are unknown, and their role in muscle disease is unclear. Here, we present biophysical/biochemical studies in muscle LIM protein (MLP) deficient cardiac muscle that support a selective role for this Z disc protein in mechanical stretch sensing. MLP interacts with and colocalizes with telethonin (T-cap), a titin interacting protein. Further, a human MLP mutation (W4R) associated with dilated cardiomyopathy (DCM) results in a marked defect in T-cap interaction/localization. We propose that a Z disc MLP/T-cap complex is a key component of the in vivo cardiomyocyte stretch sensor machinery, and that defects in the complex can lead to human DCM and associated heart failure.