| Description |
Does strain induce changes in the electrical properties of the heart? Does strain affect the microstructure of cardiac myocytes? Others have considered these questions, but have been limited in their findings. I addressed the first question by measuring conduction velocity in papillary muscles in rest conditions and during applied strain. I also applied streptomycin, a nonselective stretch ion channel blocker, in the above conditions. In control, conduction velocity increased with strain before conduction block occurred. When streptomycin was applied conduction velocity peaked at a higher strain, but conduction block remained unchanged. Changes in electrical properties of papillary muscle allowed for changes in conduction velocity. Although streptomycin did not alter the strain at which conduction block occurred, it did shift the peak conduction velocity to a higher strain. The second question was addressed by imaging isolated cardiac ventricular myocytes in varying degrees of contraction and strain using confocal microscopy. The length of transverse tubules (t-tubules), along with cross-section ellipticity, and orientation in myocytes were analyzed for cells in 16% contraction, rest, and 16% strain. Cells in contraction showed an increase in length of t-tubules with less elliptical cross-sections compared to cells in rest. Strained cells showed a decrease in length of t-tubules with less elliptical cross-sections than cells at rest. The orientation of t-tubule cross-sections changed in a similar manner when comparing contracted and strained cells with cells at rest. The transfer of strain to the t-tubule system supports the hypothesis that the motion of t-tubules during contraction and stretch may constitute a mechanism for pumping extracellular fluid. |
