Weaving hypothesis of cardiomyocyte sarcomeres: discovery of periodic broadening and narrowing of intercalated disk during volume-load change.

To investigate how cardiomyocytes change their length, echocardiographic and morphological studies were performed on rabbit hearts that were subjected to volume overload, overload removal, and repeated cycles of overload and overload removal. These conditions were created by arterio-venous fistula between the carotid artery and jugular vein, closure of the fistula, and cycles of repeatedly forming and closing fistula, respectively. After overload, hearts dilated and myocytes elongated. Intercalated disks repeatedly broadened and narrowed with a 2-day cycle, which continued for 8 weeks in many animals. The cycle consisted of shifts between five modes characterized by two interdigitation elongation-and-shortenings as follows: (I) flat with short ( approximately 1/4 to approximately 1/3 sarcomere long) interdigitations; (II) flat with long (one sarcomere long) interdigitations; (III) grooved with short interdigitations; (IV) grooved with long interdigitations; (V) flat with short interdigitations intermingled by sporadic long interdigitations; and return to (I). After overload removal, hearts contracted and myocytes shortened with similar 2-day broadening and narrowing cycle of intercalated disks, in which the five modes were reversed. Repeated overload and overload removal resulted in the repetition of myocyte elongation and shortening. We hypothesize that a single elongation-and-shortening event creates or disposes one sarcomere layer, and the two consecutive elongation-and-shortenings occur complementarily to each other so that the disks return to their original state after each cycle. Our hypothesis predicts that intercalated disks weave and unravel one sarcomere per myocyte per day.

Calcium-supplemented University of Wisconsin solution in long-term myocardial preservation.

The purpose of this study was to assess the effects of the addition of calcium to University of Wisconsin solution in long-term myocardial perfusion. In a heterotopic heart transplantation model, performed in pigs, the donor heart was preserved for 24 hours by means of continuous perfusion in this solution, without (24hUW group) or with calcium, 2.4 mmol/L (24hUW+Ca). During this period, the oxygenation and pH of the solution were measured, as were the calcium and lactate concentrations and enzyme release. After two hours of reperfusion, samples were collected from both ventricles for the morphological study. In the control group, there were no signs that reperfusion had triggered the calcium paradox. The addition of this cation to the preservation solution improved the intercellular junction integrity but, at the same time, favored intracellular calcium overload. This is manifested by increased enzyme release during preservation (LDH: 242+/-95 vs 140+/-25; CK: 668+/-371 vs 299+/-83 (U/L). p<0.01 in both cases) and signs of ventricular contracture: hardness and stiffness were significantly more prominent than in the group without calcium supplementation. Moreover, in comparison with the control group, the structural morphology of 24hUW+Ca is characterized by the more prominent and extensive presence of contraction bands and disorganized actin structure. Thus, under the experimental conditions employed in this study, we consider the addition of calcium to Wisconsin solution to be unadvisable.

Effect of 12-O-tetradecanoylphorbol-13-acetate on intercellular communication in various clones of mouse epidermal JB6 cells.

We studied gap junctional intercellular communication (IC) in various clones of mouse epidermal JB6 cells and the effect of the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA) on such communication. JB6 clones used included nonpromotable, promotable, and transformed clones, representing a spectrum in susceptibility to transformation from nontransformed, to initiated (postinitiated), to transformed cells. We used the dye transfer assay and the radioisotope transfer assay, and quantified IC both in homologous pairings, where IC among cells of a single clone was examined, and heterologous pairings, where cells of initiated or transformed clones were paired with cells of a nonpromotable clone. Both pairings showed good IC in the absence of TPA and poor IC in the presence of TPA. However, suppression of IC by TPA was more effective when cells had advanced in promotability. IC was more suppressed by TPA in heterologous pairing than in homologous pairing. These results implied that in advanced stages of promotion, the capability to retain IC with each other (homologous IC) and especially with their nontransformed counterpart (heterologous IC) is progressively lost. Thus we conclude that the interaction of initiated cells and transformed cells with nontransformed cells decreases progressively in this model system for tumor promotion and progression.