Generation of reentrant arrhythmias by dominant-negative inhibition of connexin43 in rat cultured myocyte monolayers.

AIMS: Alteration of connexin43 (Cx43)-mediated intercellular communication is known to promote susceptibility to ventricular tachyarrhythmias. However, the precise mechanism of the altered Cx43 responsible for arrhythmogenesis remains unclear. We sought to understand changes in impulse propagation of ventricular myocytes under dominant-negative (DN) inhibition of Cx43 in the development of arrhythmias. METHODS AND RESULTS: Intercellular communication was inhibited in confluent monolayers of neonatal rat cultured myocytes by an adenoviral vector-mediated gene transfer for DNCx43-fused red fluorescence protein (RFP). A high-resolution, macro-zoom fluorescence imaging system was used to visualize both the fluo4- and RFP-fluorescence intensities as measures of Ca2+ transient propagation and distribution of DNCx43 inhibition, respectively, in the myocyte monolayers. DNCx43 inhibition of the monolayers resulted in not only a significant slowing of Ca2+ transient propagation velocity, but also a preferential emergence of spiral-wave reentrant arrhythmias elicited by rapid pacing. Detailed observations on the development of spiral waves revealed that the gene-transferred myocyte monolayers exhibited regional slowing of propagation and subsequent generation of wave break, resulting in reentrant arrhythmias. Furthermore, DNCx43-RFP-transferred monolayers showed higher fluorescence intensity of RFP at the break point than at the surrounding myocardium, indicating a culprit role of DNCx43 inhibition in the genesis of spiral reentry. CONCLUSION: The present results indicate that regional heterogeneity in gap-junctional communication promotes, in addition to slowing of conduction velocity, susceptibility to reentrant tachyarrhythmias.

Ectopic cystic thymoma associated with Raynaud's phenomenon.

Mediastinal cystic tumors are well-marginated round lesions that comprise 12% to 18% of all mediastinal masses. These lesions include a variety of diseases with overlapping radiologic appearances and variable prognoses. Pathological examinations are almost always required for differential diagnosis. We encountered a case of anterior mediastinal tumor discovered in the process of investigation of Raynaud's phenomenon. Taking into account the tumor location, a pericardial cyst was initially suspected. However, the tumor was surgically resected and histopathological examinations demonstrated thymus-like tissue in the cyst walls. Raynaud's phenomenon greatly improved after surgery. These findings suggested that cystic thymoma originated from ectopic thymic tissue and is accompanied by paraneoplastic syndrome.

[A case of "Takotsubo" cardiomyopathy observed with myocardial scintigraphy from the acute phase].

A 57-year-old woman was emergently admitted to our hospital because of chest oppression. On examination, blood pressure was 174/96 mmHg, pulse rate was 90/min and coarse crackle and third heart sound were audible. On laboratory data, the levels of LDH and CPK-MB were mildly elevated. Electrocardiogram (ECG) demonstrated elevation of the ST segment in leads I, aVL and V2-V5. 99mTc-tetrofosmin myocardial SPECT (TF) showed severely reduced uptake in the apex and anterior wall. Emergent coronary angiography (CAG) did not show any stenotic lesion. Left ventriculography (LVG), however, demonstrated akinesis of the apex, anterior, and inferior walls, and basal hyperkinesis. On the second hospital day, ECG demonstrated inverted T wave in leads I, aVL and V2-V5. 123I-BMIPP myocardial SPECT (BMIPP) and 123I-MIBG myocardial SPECT (MIBG) were performed on the second and fourth hospital days, respectively. These cardiac images showed severely reduced uptake equally. TF, BMIPP, and MIBG were re-examined on the eighth, tenth, and twelfth hospital days, respectively. MIBG, BMIPP, and TF showed reduced uptake in order of severity. On the fourteenth hospital day, CAG and LVG were re-examined. Coronary vasospasm provocation test was negative using ergonovine and acetylcholine, and LVG did not demonstrated any sign of asynergy. We considered that this case was "Takotsubo" cardiomyopathy and might be caused by microvascular spasm.

[Serial change of myocardial fatty acid metabolism in a case with severe myocardial ischemia].

A 66-year-old-man was admitted to our hospital because of chest pain on effort in October 1999. The initial images of 123I-BMIPP myocardial SPECT (BM) showed moderately decreased tracer uptake in the apex and the delayed images revealed redistribution in the apex. Coronary angiography revealed 99% stenosis in the proximal portion of the left anterior descending artery. Since sudden onset anaphylactic shock induced by contrast media developed, so percutaneous transluminal coronary angioplasty was not performed. The patient's symptoms were improved with medical treatment. On BM in March 2000, the initial images indicated slightly reduced uptake in the apico-anteroseptal region and the delayed images revealed mildly redistribution in the same area. BM in September 2000, the initial images showed moderately reduced uptake in the apico-anteroseptal region and the delayed images revealed high washout in the same area. The patient's symptoms markedly deferiorrated in March 2001, and BM initial images revealed slightly reduced uptake in the apico-anteroseptal region and the delayed images revealed redistribution in the same area again. During the clinical course, electrocardiography and 99mTc-tetrofosmin myocardial SPECT revealed no marked changes. We consider that 123I-BMIPP myocardial SPECT is useful in estimating myocardial ischemia.

Multiphoton excitation-evoked chromophore-assisted laser inactivation using green fluorescent protein.

Noninvasive, straightforward methods to inactivate selected proteins in living cells with high spatiotemporal resolution are needed. Chromophore-assisted laser inactivation (CALI) can be used to photochemically inactivate proteins, but it has several drawbacks, such as procedural complexity and nonspecific photodamage. Here we show that by application of multiphoton excitation to CALI, enhanced green fluorescent protein (EGFP) is an effective chromophore for inactivation of a protein's function without nonspecific photodamage in living mammalian cells.

In situ Ca2+ dynamics of Purkinje fibers and its interconnection with subjacent ventricular myocytes.

Purkinje fibers play essential roles in impulse propagation to the ventricles, and their functional impairment can become arrhythmogenic. However, little is known about precise spatiotemporal pattern(s) of interconnection between Purkinje-fiber network and the underlying ventricular myocardium within the heart. To address this issue, we simultaneously visualized intracellular Ca(2+) dynamics at Purkinje fibers and subjacent ventricular myocytes in Langendorff-perfused rat hearts using multi-pinhole type, rapid-scanning confocal microscopy. Under recording of electrocardiogram at room temperature spatiotemporal changes in fluo3-fluorescence intensity were visualized on the subendocardial region of the right-ventricular septum. Staining of the heart with either fluo3, acetylthiocholine iodide (ATCHI), or di-4-ANEPPS revealed characteristic structures of Purkinje fibers. During sinus rhythm (about 60 bpm) or atrial pacing (up to 3 Hz) each Purkinje-fiber exhibited spatiotemporally synchronous Ca(2+) transients nearly simultaneously to ventricular excitation. Ca(2+) transients in individual fibers were still synchronized within the Purkinje-fiber network not only under high-K(+) (8 mM) perfusion-induced Purkinje-to-ventricular (P-V) conduction delay, but also under unidirectional, orthodromic P-V block produced by 10-mM K(+) perfusion. While spontaneous, asynchronous intracellular Ca(2+) waves were identified in injured fibers of Purkinje network locally, surrounding fibers still exhibited Ca(2+) transients synchronously to ventricular excitation. In summary, these results are the first demonstration of intracellular Ca(2+) dynamics in the Purkinje-fiber network in situ. The synchronous Ca(2+) transients, preserved even under P-V conduction disturbances or under emergence of Ca(2+) waves, imply a syncytial role of Purkinje fibers as a specialized conduction system, whereas unidirectional block at P-V junctions indicates a substrate for reentrant arrhythmias.