Osami Kohmoto

Targeted Disruption of Na+/Ca2+ Exchanger Gene Leads to Cardiomyocyte Apoptosis and Defects in Heartbeat

Ca2+, which enters cardiac myocytes through voltage-dependent Ca2+channels during excitation, is extruded from myocytes primarily by the Na+/Ca2+ exchanger (NCX1) during relaxation. The increase in intracellular Ca2+ concentration in myocytes by digitalis treatment and after ischemia/reperfusion is also thought to result from the reverse mode of the Na+/Ca2+ exchange mechanism. However, the precise roles of the NCX1 are still unclear because of the lack of its specific inhibitors. We generated Ncx1-deficient mice by gene targeting to determine the in vivo function of the exchanger. Homozygous Ncx1-deficient mice died between embryonic days 9 and 10. Their hearts did not beat, and cardiac myocytes showed apoptosis. No forward mode or reverse mode of the Na+/Ca2+ exchange activity was detected in null mutant hearts. The Na+-dependent Ca2+ exchange activity as well as protein content of NCX1 were decreased by ∼50% in the heart, kidney, aorta, and smooth muscle cells of the heterozygous mice, and tension development of the aortic ring in Na+-free solution was markedly impaired in heterozygous mice. These findings suggest that NCX1 is required for heartbeats and survival of cardiac myocytes in embryos and plays critical roles in Na+-dependent Ca2+ handling in the heart and aorta.

Molecular cloning and expression of inducible nitric oxide synthase in chick embryonic ventricular myocytes.

OBJECTIVE Inducible nitric oxide synthase (iNOS) has been implicated to contribute to myocardial dysfunction in various settings, but considerable species differences have been noted in the levels of iNOS expression and its function in several tissues. The aim of this study was to elucidate evolutional changes in myocardial iNOS expression and function. METHODS An iNOS cDNA clone was isolated by RT-PCR from the 10-day old cultured chick embryonic ventricular myocytes stimulated with 10 micrograms/ml of lipopolysaccharide. Expression of the iNOS mRNA was analyzed with Northern blot analysis and RNase protection assay. The iNOS activity was estimated from conversion rates of L-arginine to L-citrulline and intracellular cGMP contents were measured with radioimmunoassay. Furthermore, both [Ca2+]i (fluorescent dye indo-1) and cell contraction (video motion detector) were simultaneously recorded. RESULTS Aside from the primer sequences, the insert (1026 bp) of the cDNA clone showed 66.4% identity at the deduced amino acid level to the human iNOS cDNAs. Northern blot analysis revealed that chicken iNOS mRNA of approximately 4.5 kb was induced by lipopolysaccharide within 6 h in the cultured myocytes. RNase protection assay also showed that lipopolysaccharide provoked 14.6 +/- 5.1-fold increases (n = 6, p < 0.05) in the iNOS mRNA signals within 6 h. The iNOS activity (+300%, P < 0.05) as well as the intracellular cGMP contents (+75%, P < 0.01) were significantly augmented in the lipopolysaccharide-stimulated cells. Both the cell contraction and [Ca2+]i were significantly reduced after the administration of a large amount (10 mM) of L-arginine in the myocytes pretreated with both lipopolysaccharide and NG-monomethyl-L-arginine (100 microM). CONCLUSION As like as the nucleotide and amino acid sequences, the myocardial effects of the iNOS may also be evolutionary conserved.

Successful bridge to resynchronization therapy with a left ventricular assist system in a patient with idiopathic dilated cardiomyopathy

Implantation of a left ventricular assist system (LVAS) in patients with idiopathic dilated cardiomyopathy (DCM) may improve cardiac function and allow explantation of the device. Generally, an ejection fraction of more than 40% is considered necessary for successful weaning from an LVAS, but less than 10% of DCM patients with an LVAS can achieve such a significant recovery of cardiac function. Cardiac resynchronization therapy, or atrial-synchronized biventricular pacing, has been found to treat congestive heart failure and ventricular dyssynchrony effectively. Here we report on a patient with an LVAS, in whom enough functional recovery could be obtained with resynchronization therapy for the device to be explanted successfully. A 32-year-old man was implanted with a Toyobo-NCVC paracorporeal LVAS to treat his intractable heart failure caused by idiopathic dilated cardiomyopathy. While on the LVAS for 8 months, his cardiac function recovered to some extent. The ejection fraction of his left ventricle (LVEF) improved from 9% to 41%. He chose explantation of the device rather than heart transplantation. Because he occasionally showed a wide QRS pattern on his ECG, epicardial biventricular pacing leads as well as a biventricular pacemaker were implanted on LVAS explantation surgery. An echocardiogram 2 weeks after explantation showed a marked difference in his LVEF by switching his biventricular pacing on and off (40% with biventricular pacing on and 29% with it off). Biventricular pacing may help recovery of cardiac function in selected LVAS patients and contribute to the increase in bridge to recovery cases.

Severe pulmonary stenosis and aortopulmonary fistula caused by a dissecting aneurysm in the ascending aorta

Discussion Surgical repair of aortic coarctation has expanded to include resection with end-to-end anastomosis, prosthetic patch aortoplasty, subclavian flap aortoplasty, and aortic resection with graft replacement. Because further aortic growth is not a problem in adult patients, graft replacement or bypass is often used and produces the best results. As the aortic wall in the portion of coarctation was thought to be fragile in our case because of the median necrosis, we used an open proxymal anastomosis technique to avoid possible aortic injury caused by crossclamping. The central cannulation technique is preferred for correction of postductal coarctation of the aorta to secure sufficient cerebral perfusion. In our case, this technique also had the advantage of preventing scattering of debris by the blood jet in an aortic aneurysm to cerebral blood flow. We prefer insertion of a venous cannula into the right atrium through the right femoral vein rather than insertion into the main pulmonary artery, as originally reported by Westaby and colleagues, because we have sometimes found that the wall of the main pulmonary artery is very fragile and thus susceptible to injury. We routinely insert a double-staged venous cannula through the right femoral vein in operations for descending aortic aneurysms and have experienced no technical problems. In conclusion, our “modified” central cannulation technique and open proxymal anastomosis technique seem to be safe. This is an appropriate approach for surgical correction, and we recommend it as the standard approach for the coarctation of the aorta in adults.

Discrepancy Between Slow Relaxation and Increased Myocardial Stiffness

The time constant of left ventricular pressure fall (TB, P = P0 + A. e-t /TB) is a good indicator of myocardial relaxation, but the physiological nature of the asymptote (P0) is not yet clear. The effects of hypoxia and the combined effects of hypoxia and DPI 201-106 (DPI, 10-6 M and 3 × 10-6 M), a new cardiotonic agent which increases the sensitivity of contractile elements to Ca2+, on diastolic myocardial function in isolated isovolumic rabbit hearts were investigated. There were close correlations between the change in left ventricular end-diastolic pressure (⊿A LVEDP) and ⊿P0 (r = 0.98, P < 0.01) and between ⊿TB and ⊿LVEDP (r = 0.73, P < 0.01) following hypoxia. The combination of hypoxia and DPI induced further increments in LVEDP (25 ± 8 mmHg, P < 0.05 vs hypoxia) and P0 (15 ± 7 mmHg, P < 0.05), and still there was a close linear correlation between ⊿LVEDP and ⊿P0 (y = 1.08x + 1.5, r = 0.90, P < 0.05). However, TB(52 ± 12 ms) was not altered and no relationship was observed between ⊿TB and ⊿LVEDP.