Contractile function of isolated feline cardiocytes in response to viscous loading.

The classical force-velocity relationship is a standard measure of the contractile function of isolated linear cardiac muscle, but no such simple index of contractile function exists for the isolated mammalian cardiocyte. Therefore, this study established an analogous viscosity-velocity relationship for the characterization of cardiocyte contractile function. For this purpose, force was imposed on unfettered adult feline cardiocytes as a series of defined viscous loads, which provided resistance to cardiocyte shape changes during contraction. This was done by increasing the viscosity of the Krebs superfusate (37 degrees C, pH 7.4) in graded, reproducible steps from 1 to 500 centipoise by the addition of methylcellulose. Sarcomere motion within each contracting cardiocyte was measured as movement of the diffraction pattern cast onto a photodiode array by a laser beam passing through the cell. Both the rate and extent of sarcomere shortening varied inversely with increasing viscosity, whereas neither resting sarcomere length nor osmolarity was altered. Further, increased inotropism effected by paired-pulse stimulation of cardiocytes caused an upward shift of the entire viscosity-velocity relationship. Thus the cardiocyte viscosity-velocity relationship is analogous in form to the force-velocity relationship of isolated linear cardiac muscle and provides a simple reproducible method for characterizing the contractile performance of relatively large numbers of cardiocytes isolated from a single specimen of myocardium.

The platelet strip. I. A low-fibrin contractile model of thrombin-activated platelets.

The ultrastructure and contractile behavior of a new preparation of thrombin-activated human platelets is described. The preparation is referred to as the "platelet strip" because of its similarities to classical vascular smooth muscle strips. The platelet strip consists of a giant platelet aggregate 10 mm long, 4 mm wide, and 200 micron thick. To facilitate handling, the aggregate has a special high-compliance nylon mesh embedded in its mass. Each strip contains 7.3 X 10(8) platelets. Fibrin contamination is 150-fold lower than in platelet-rich plasma clots. Active isometric forces of up to 100 g/cm2 and 6-10 h viability are easily and reproducibly obtained. Platelet strips remain contracted after thrombin activation. The contraction is tonic and partial. Further small increases in force can be produced by depolarizing solutions or pharmacological agents, e.g., ADP, epinephrine, and endoperoxide analogues. These small increases are reversible on washout of the agents. Full relaxation is induced by agents such as prostaglandin E1 or papaverine, which increase adenosine 3',5'-cyclic monophosphate. However, after washout of these agents, recovery of tension is variable depending on the concentration of the drug and the degree of prestretching of the preparation.

Infrared video pupillometry: a method used to measure the pupillary effects of drugs in small laboratory animals in real time.

Pupillometry in clinical investigation and in basic research often requires dynamic measurement of pupil size. Static methods, i.e. direct observation and still photography, are often used because of the high cost of commercial infrared pupillometers and problems with pupil-iris contrast in small animals. This report describes an improved infrared video pupillometer (IVP) which accurately measures the pupil area of small animals in real time (30 samples/sec). Two components of the pupillometer were designed and built by the authors: a "bright-pupil" infrared illumination system and a digital video signal processor (VSP). The use of a standard closed-circuit television camera to produce the pupil image signal results in a device that is relatively economical to construct. The IVP is sensitive enough to accurately track pupil are in the study of the pupil light reflex or pupillary oscillations. Several applications for the IVP are illustrated, including analysis of the transient response to light flashes and intravenous injections of drug, and analysis of the spontaneous and drug-induced pupillary fluctuation. Pupillography has been applied in the bioassay of various psychopharmacologic compounds and in the assessment of narcotic dependency. This IVP is being used in this laboratory to study the pupillary action of opiates in the rabbit and rat.