Cross-talk between beta(1)-adrenoceptors and ET(A) receptors in modulation of the slow component of delayed rectifier K(+) currents

Nitric oxide down-regulates voltage-gated Na+ channel in cardiomyocytes possibly through S-nitrosylation-mediated signaling

Nitric oxide (NO) is produced from endothelial cells and cardiomyocytes composing the myocardium and benefits cardiac function through both vascular-dependent and—independent effects. This study was purposed to investigate the possible adverse effect of NO focusing on the voltage-gated Na⁺ channel in cardiomyocytes. We carried out patch-clamp experiments on rat neonatal cardiomyocytes demonstrating that NOC-18, an NO donor, significantly reduced Na⁺ channel current in a dose-dependent manner by a long-term application for 24 h, accompanied by a reduction of Nav1.5-mRNA and the protein, and an increase of a transcription factor forkhead box protein O1 (FOXO1) in the nucleus. The effect of NOC-18 on the Na⁺ channel was blocked by an inhibitor of thiol oxidation N-ethylmaleimide, a disulfide reducing agent disulfide 1,4-Dithioerythritol, or a FOXO1 activator paclitaxel, suggesting that NO is a negative regulator of the voltage-gated Na⁺ channel through thiols in regulatory protein(s) for the channel transcription.

Insulin suppresses IKs (KCNQ1/KCNE1) currents, which require β-subunit KCNE1

Abnormal QT prolongation in diabetic patients has become a clinical problem because it increases the risk of lethal ventricular arrhythmia. In an animal model of type 1 diabetes mellitus, several ion currents, including the slowly activating delayed rectifier potassium current (IKs), are altered. The IKs channel is composed of KCNQ1 and KCNE1 subunits, whose genetic mutations are well known to cause long QT syndrome. Although insulin is known to affect many physiological and pathophysiological events in the heart, acute effects of insulin on cardiac ion channels are poorly understood at present. This study was designed to investigate direct electrophysiological effects of insulin on IKs (KCNQ1/KCNE1) currents. KCNQ1 and KCNE1 were co-expressed in Xenopus oocytes, and whole cell currents were measured by a two-microelectrode voltage-clamp method. Acute application of insulin suppressed the KCNQ1/KCNE1 currents and phosphorylated Akt and extracellular signal-regulated kinase (ERK), the two major downstream effectors, in a concentration-dependent manner. Wortmannin (10(-6) M), a phosphoinositide 3-kinase (PI3K) inhibitor, attenuated the suppression of the currents and phosphorylation of Akt by insulin, whereas U0126 (10(-5) M), a mitogen-activated protein kinase kinase (MEK) inhibitor, had no effect on insulin-induced suppression of the currents. In addition, insulin had little effect on KCNQ1 currents without KCNE1, which indicated an essential role of KCNE1 in the acute suppressive effects of insulin. Mutagenesis studies revealed amino acid residues 111-118 within the distal third C-terminus of KCNE1 as an important region. Insulin has direct electrophysiological effects on IKs currents, which may affect cardiac excitability.

Effects of endothelin-1 on the relaxation of rat coronary arteries

To analyze the effects of endothelin-1 on the b-adrenergic response of the coronary circulation, 2-mm-long segments of coronary arteries from rats were prepared for isometric tension recording in organ baths. The relaxation to isoproterenol (3 x 10(-8) M), field electrical stimulation (4 Hz, 0.1-millisecond duration, 10 seconds), acetylcholine (3 x 10(-8) M), and sodium nitroprusside (10(-9) M) was recorded in arteries precontracted with U46619 (10(-7) to 5 x 10(-7) M) before and after treatment with endothelin-1 (3 3 10210 and 1029 M). The relaxation to isoproterenol was increased by treatment with endothelin-1 and with the endothelin ET(B) antagonist BQ788 (10(-6) M) but not with the endothelin ET(A) antagonist BQ123 (10(-6) M) or with the blocker of protein kinase C chelerythrine (10(-5) M). In the presence of BQ788, BQ123, or chelerythrine, endothelin-1 did not modify the relaxation to isoproterenol. Treatment with endothelin-1 did not modify the relaxation to electrical stimulation, acetylcholine, or sodium nitroprusside. These results suggest that endothelin-1 may potentiate coronary beta-adrenergic vasodilatation, at least in part due to stimulation of endothelin ET(A) receptors and activation of protein kinase C.

Cardiac ion channel gene mutations in sudden infant death syndrome

Sudden infant death syndrome (SIDS) is multifactorial and may result from the interaction of a number of environmental, genetic, and developmental factors. We studied three major genes causing long QT syndrome in 42 Japanese SIDS victims and found five mutations, KCNQ1-K598R, KCNH2-T895M, SCN5A-F532C, SCN5A-G1084S, and SCN5A-F1705S, in four cases; one case had both KCNH2-T895M and SCN5A-G1084S. All mutations were novel except for SCN5A-F532C, which was previously detected in an arrhythmic patient. Heterologous expression study revealed significant changes in channel properties of KCNH2-T895M, SCN5A-G1084S, and SCN5A-F1705S, but did not in KCNQ1-K598R and SCN5A-F532C. Our data suggests that nearly 10% of SIDS victims in Japan have mutations of the cardiac ion channel genes similar to in other countries.

Mutations in the SLC34A2 gene are associated with pulmonary alveolar microlithiasis

RATIONALE

Pulmonary alveolar microlithiasis is an autosomal recessive disorder in which microliths are formed in the alveolar space.

OBJECTIVES

To identify the responsible gene that causes pulmonary alveolar microlithiasis.

METHODS

By means of a genomewide single-nucleotide polymorphism analysis using DNA from three patients, we have narrowed the region in which the candidate gene is located. From this region, we have identified a gene that has mutations in all patients with pulmonary alveolar microlithiasis.

MEASUREMENTS AND MAIN RESULTS

We identified a candidate gene, SLC34A2, that encodes a type IIb sodium phosphate cotransporter and that is mutated in six of six patients investigated. SLC34A2 is specifically expressed in type II alveolar cells, and the mutations abolished the normal gene function.

CONCLUSION

Mutations in the SLC34A2 gene that abolish normal gene function cause pulmonary alveolar microlithiasis.