Abstract
Single adult cardiac ventricular cells were prepared by collagenase perfusion of a rat heart. They were stimulated electrically in a perfusion chamber and their length changes were followed under a microscope. The motion was followed via a video camera and by a TV-line counting device and was recorded on-line by a personal computer. The program RECORD was used to calculate peak amplitude, base line drift and peak width at different peak heights allowing the determination of a number of variables of the cellular motion. The method was applied to drugs affecting the amplitude of contractions and the speed of relaxation. Results of beta-adrenergic stimulation, muscarinic inhibition and of the Ca(2+)-ATPase inhibitor cyclopiazonic acid (CPA) are shown. Besides its stimulatory effect on length, the beta-adrenergic agonist isoprenaline concentration-dependently shortened relaxation time. Carbachol reversed the increase in cellular shortening caused by isoprenaline in a concentration-dependent manner without fully reversing the shortened relaxation. CPA prolonged the return to diastole, presumably due to its inhibition of Ca(2+)-reuptake into the sarcoplasmatic reticulum.
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