Right ventricular contractile protein function in rats with left ventricular myocardial infarction

We studied contractile function in cardiac trabeculae isolated from the right ventricles (RV) of rats with experimental heart failure (HF) induced by left ventricular (LV) myocardial infarction (24 wk post-MI; n = 6) and from sham-operated rats (n = 7). Sarcomere length (SL) was measured by laser diffraction techniques, and force (F) was measured by silicon strain gauge. SL was kept constant at all times by computer feedback control. HF was associated with marked LV dilation and pulmonary congestion. In intact, RV twitching trabeculae, HF was associated with a depression of the F-SL relation at extracellular Ca2+ concentration ([Ca2+]o) = 1.5 mM and a depression of the F-[Ca2+]o relation at SL = 2.0 microns. HF was also associated with a significant depression of the F-intracellular [Ca2+] relation at SL = 2.0 microns measured after chemical permeabilization of these RV trabeculae (skinned fibers). Our results suggest that reduced force development in this model of HF is due, in part, to depressed function of the contractile filaments.

Permeabilization of Piceaglauca protoplasts to macromolecules

Chemical permeabilization (polyethylene glycol, molecular weight 3350) and electropermeabilization (electroporation) treatments were applied to white spruce protoplasts to determine their effectiveness for uptake of membrane impermeable macromolecules. The two techniques have been compared using the membrane impermeable fluorescent dye calcein (molecular weight 622). The effects of varying the polyethylene glycol concentration, or the capacitance and voltage, were tested. In both techniques, the viability of protoplasts decreased after treatment compared with the controls. However, electroporation (capacitance 25 μF; voltage 300 V, 750 V•cm−1) gave better-permeabilization results (55% protoplast viability with 96% of these being fluorescent protoplasts) than the best treatment with polyethylene glycol (20%) (30% protoplast viability with 15% being fluorescent protoplasts). An investigation was made with the dye fluorescein isothiocyanate dextrans at different average molecular weights: 4000, 70 000, and 150 000. The degree of internalization by electroporation of each of these molecules did not substantially differ, though they were all low compared with calcein, which is suggestive of a limitation in permeability. The protoplasts subjected to either polyethylene glycol or electroporation treatments gave rise to callus and proembryos.