MEASUREMENT OF INOTROPIC EFFECTS BY A NEWLY DEVELOPED GUINEA-PIG PAPILLARY-MUSCLE BIOASSAY

In order to measure inotropic influences of physiologically occurring substances and drugs we used a newly developed guinea pig papillary mu scle (GPPM) bioassay. GPPM were suspended in air and surface coated wi th buffer (Krebs-Henseleit solution). The muscles were stimulated (pul sating direct current, 1.5 V; 0.5 Hz, 20 ms duration) which led to con traction. This method enables measurements of inotropic effects up to 5 days, contrary to previous studies (1 day), in which immersions of G PPM in buffer were performed. In order to investigate the comparabilit y of the new method we measured the effect of metabolites (citric acid cycle), lactic acid, lactate, and extracellular pH on muscle contract ility. The H+-dependent decrease of the contractile force of the GPPM can be compensated by an increased Ca2+-concentration. Further, the in fluence of catecholamines (isoproterenol) on the contractility was inv estigated. As a result, isoproterenol caused arrhythmias and extrasyst oles as it was observed in clinical studies. Several pharmaceutical su bstances were tested to show the reproducibility and repeatability of the bioassay.