PASSIVE VENTRICULAR MECHANICS IN TIGHT-SKIN MICE

Although changes in the extracellular matrix have been associated with changes in ventricular compliance in certain diseased states, this re lationship has not been entirely established. Accordingly, we studied passive ventricular mechanics in the tight-skin (TSk) mouse, a mutant strain known to have increased cardiac collagen. In the arrested left ventricle, we determined the pressure-volume relationship and the stre ss-free state, as defined by the ''opening angle'' of an equatorial ri ng with a radial cut. The results showed the mean opening angle in the TSk mouse to be smaller than that in phenotypic negative controls (7 +/- 6 vs. 21 +/- 9 degrees), and there was no statistical difference i n the pressure-volume curves. Histological quantification of the trans mural collagen showed a uniform increase of collagen area fraction acr oss the wall in TSk mouse, and a significantly thicker superficial epi cardial collagen layer (4.68 +/- 0.87 vs. 3.34 +/- 0.76 mu m). Thus, a lthough there appears to be a decrease of residual stress in the TSk m ouse heart, which may be related to the thicker epicardial collagen la yer, the combination of increased myocardial collagen and the change i n stress-free state did not seem to affect the passive pressure-volume relationship of the left ventricle.