Length, width, and volume changes in osmotically stressed myocytes.

Sarcomere lengths, cell widths, and cell volumes were determined from photomicrographs and direct optical imaging of Ca2+-tolerant myocytes dispersed from collagenase-perfused whole rat myocardium. Individual unattached cells were examined at rest first in the normosmotic Ca2+-Tyrode saline solution and then in a sequence of hypotonic or hypertonic Tyrode solutions. Myocytes swell and shrink in hypotonic and hypertonic media but not as much as expected for an ideal uniform osmotic system. Furthermore, these changes were not proportional in the longitudinal and radial directions. These data suggest an 18% osmotically inactive volume and significant internal radial and longitudinal load-bearing structures within these cardiac myocytes.