ИСТИНА

It is well established that interstitial edema (IE), common to various cardiac pathologies, can disrupt myocardial function by affecting cell-to-cell coupling. However, the effect of IE on structural integrity of t-tubular system and the ion-channel function within is unknown. To that end we used a combination of loose patch action potential (AP) recording and confocal Ca2+ imaging in Langendorf-perfused rat hearts. IE was induced by increasing the osmolarity of the perfusion solution with mannitol (56 mM/L). Extracellular micro-electrode mapping of the surface of myocytes within the ventricular epicardium reveled two types of APs: a fast single phase negative signal (AP1) and a composite negative signal that in addition to the fast signal present in AP1 showed two slower components (i.e. intermediate and delayed) (AP2). Pharmacological analysis demonstrated that the fast component of both AP1 and AP2 was mediated by opening of tetrodotoxin (TTX)-resistant Na+ channels. On the other hand, the intermediate component of AP2 was attributed to activity of both L-type Ca2+ channels and TTX-sensitive Na+ channels. Lastly, the delayed component of AP2 reflected Na+Ca2+ exchange activity. Of note, IE resulted in a gradual inhibition of the intermediate and delayed phases of AP2 without a significant effect on the fast component of AP1 and AP2. Confocal microscopy performed in hearts stained with rhodamine B demonstrated that IE caused also a profound disruption of t-tubule structure, including vacuolization and sealing of t-tubule openings. Thus, in this study we show, for the first time, electrical signals that mark activities of ion transport mechanisms localized in the cardiac t-tubules, including L-type Ca2+ channels, TTX-sensitive Na+ channels, and Na+/Ca2+ exchange. We also demonstrate that acute myocardial edema disrupts the structural continuity of t-tubules and compromises the functional activity of these ion transport systems.