Stimulation pattern dependent contractions of myocardial preparations after lipid diets

Lipid diets modify the electro-mechanical coupling. To characterize the regulation of the supply of Ca for the activation of the contraction the influence of the stimulation pattern on the development of tension was investigated after diets containing cholesterol (Ch), rape oil (RO) and cholesterol-oil (ChO). The sequence of increasing inotropic states produced was compared with a control group (C). In ChO high resting potentiation, low postextrastimulatory potentiation (PEP) and a delayed Ca supply for interpolated extra contractions (EC) are typical features. The positive inotropic effect of rising extracellular Ca grows parallel to the sequence of the inotropic states. The maximum rate of contraction and relaxation correlates linearly with the tension development. Some of the results are similar in RO. In both groups a more pronounced involvement of the sarcoplasmic reticulum in the Ca regulation should be responsible for the effects. Especially in C the Ca loading effect of paired stimulation shortens the latent period and increases the rate of contraction and relaxation. In Ch the highest values of PEP are reached. These results reflect the involvement of a high sarcolemmal fraction of Ca in the activation.