RESUMEN
This report describes a Langendorff heart preparation, which utilizes frog rather than mammalian hearts to demonstrate both mechanical and electrical events of the cardiac cycle. The preparation is durable in that it can be maintained for several hours while being perfused with room-temperature solutions that are not supplemented with oxygen. Ventricular perfusion is achieved via a fluid-filled reservoir coupled to a truncus arteriosus catheter advanced into the ventricle. By varying the height of the reservoir relative to the heart, changes in ventricular pressure and the rate of ventricular pressure change during systole can be recorded by way of a side port on the catheter tubing. The former is indicative of Starling's law of the heart, whereas the latter is reflective of the contractility. Electrical activity of the heart can be observed by measuring injury potentials via a needle electrode inserted into the ventricle. These are extracellular potentials that reflect ventricular action potentials. In addition, surface electrodes placed on the ventricle can be used to detect an integrated ventricular electrocardiogram. Recording of ventricular pressure simultaneously with at least one of these two electrical recordings allows a direct comparison of electrical and mechanical events of the heart. In summary, the Langendorff frog heart preparation is economical in terms of both financial cost and simplicity; yet it enables a thorough examination of both electrical and mechanical properties of the heart either as a student lab exercise or as a classroom demonstration.
Asunto(s)
Corazón/fisiología , Fisiología/educación , Enseñanza/métodos , Animales , Electrofisiología/instrumentación , Electrofisiología/métodos , Técnicas In Vitro , Contracción Miocárdica , Ranidae , Función VentricularRESUMEN
The satisfactory analysis of the Na/K ATPase, its pumping component and the mechanism of action of the inhibitor digitalis remains elusive; yet the controversial inotropic effect of digitalis in the clinical setting has been known for over a century. There are also conflicting reports of the effect of urea and uremia on the cardiovascular system, and the evidence as it exists, suggests that urea may have two effects on the intact heart, by virtue of its extent of action on hydrogen bonding of water molecules, determined by which type of muscle constitutes the myocardium. If different types of myocardium do exist, they could well respond differently to inotropic agents. Evidence suggests that two types of myocardia, relatively stress resistant or susceptible may exist, analagous to known skeletal muscle differences.
Asunto(s)
Modelos Biológicos , Miocardio/metabolismo , Estrés Fisiológico/metabolismo , Animales , Calcio/metabolismo , Cardiotónicos/farmacología , Humanos , Contracción Miocárdica/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Urea/farmacologíaRESUMEN
The intensity of light scattered at 90 degrees to the incident beam and the effective hydrodynamic radii of mitochondria incubated under a variety of conditions have been measured. Addition of high concentrations of uncouplers to respiring mitochondria resulted in a decrease in scatter which was not due to swelling. Addition of valinomycin to mitochondria depleted to substrate in K+-free medium produced an increase in scatter that was not due to shrinking. It is concluded that changes in the intensity of scattered light are not reliable indices of changes of volume of mitochondria, and the changes in conformation with changes in metabolic state dominate changes in light scatter. A molecular mechanism for the effect of metabolic state upon the scattered intensity is suggested.
Asunto(s)
Mitocondrias Hepáticas/ultraestructura , Animales , Luz , Mitocondrias Hepáticas/efectos de los fármacos , Dilatación Mitocondrial , Consumo de Oxígeno , Ratas , Dispersión de Radiación , Valinomicina/farmacologíaAsunto(s)
Glicósidos Digitálicos/farmacología , Digitalis , Corazón/fisiología , Plantas Medicinales , Plantas Tóxicas , Animales , Calcio/metabolismo , Glicósidos Digitálicos/uso terapéutico , Corazón/efectos de los fármacos , Corazón/fisiopatología , Insuficiencia Cardíaca/tratamiento farmacológico , Humanos , Enlace de Hidrógeno , ATPasa Intercambiadora de Sodio-Potasio/metabolismoRESUMEN
A new instrument is described which simplifies the measurement of the oxygen-hemoglobin dissociation curve, using small volumes of blood. An oxygen electrode, as the plunger of a syringe accommodating increasing volumes of blood at predetermined levels of saturation with oxygen, measures the amount of dissolved oxygen in the plasma, which is proportional to the gas tension.