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The conductance catheter has gained momentum since its introduction in cardiovascular dynamics back in 1980. However, measuring errors are still blurring its clinical acceptance. The main objective here was to study the effects of the injected saline concentration and temperature on the evaluation of the parallel conductance, [G.sub.p], and thus, on the correction volume [V.sub.p]. That conductance, [G.sub.p], and its associated volume, [V.sub.p], were computed using 167 saline dilution curves obtained with boluses at different concentrations and temperatures, injected in seven anesthetized closed-chest dogs. The excursion of the total conductance relative to the steady-state value during a saline maneuver showed good correlation with the injected concentration at both studied temperatures. The reference parallel volume (one reference per dog) was defined as the average value obtained with three successive maneuvers, at 6-M concentration and at body temperature; therefore, the method acted as its own reference. The variation of [V.sub.p] relative to the reference value was clearly dependent on the injected concentration and on its temperature; dispersion was greater at 22 [degrees] C than at 40 [degrees] C. The variability would recognize also other causes, such as uncertainty of the extrapolation procedure and the thoracic redistribution of electrical field lines. As conclusion, it is recommended to characterize each maneuver by its concentration and temperature. Body temperature and 6-M concentration appear as the most recommendable combination for the injectate in most animals. Finally, these results intend to characterize the [V.sub.p] estimation procedure in order to minimize errors. The variability of [V.sub.p], in different experimental conditions, demonstrated that both concentration and temperature are additional parameters that may modify the [G.sub.p] estimate. Index Terms - Conductance catheter, impedance volumetry, left ventricular volume, parallel volume, saline indicator method.

An experiment was conducted to investigate the role of the transient outward current (Ito) in the sinoatrial node by blocking the current with 4-aminopyridine in small ball-like tissue preparations from different regions of the rabbit sinoatrial node. It was shown for the first time ever that 4-aminopyridine-sensitive current plays a significant part in the electrical activity of the sinoatrial node and that this function differs from the periphery to the center and from the superior part of the sinoatrial node to the inferior part.

A study was conducted to molecularly clone and sequence canine cDNA for an isoform of nitric oxide synthase (iNOS) from explanted canine aortic smooth muscle cells. The use of the cloned product of the gene identified in the experiment will enable future studies to specifically address differential regulation of NOS isoforms in vivo as they may be expressed during allograft rejection, vascular remodeling and/or response to injury.

Carnitine plays an essential role in the regulation of long-chain fatty acid metabolism in skeletal and cardiac muscle, a process that is mediated by well-characterized enzymatic mechanisms. Here, Irving Fritz and Edoardo Arrigoni-Martelli review the evidence that carnitine and its O-acyl derivatives also influence membrane fluidity, ion channel functions, smooth muscle contractility, membrane stability and cardiac functions. The authors present the view that direct interactions of carnitine derivatives with cell membranes are independent of reactions catalysed by carnitine acyltransferases. They propose that the novel actions discussed are implicated in the mechanisms by which carnitine and its derivatives protect perfused hearts subjected to ischaemia or to oxidative stress, and help people suffering from certain types of myocardial ischaemia or peripheral arterial disease.