We measured regional distribution of xenon-133 boli at 0.25, 0.75, and 1.5 l/s in four normal seated subjects during inspirations performed predominantly with intercostal and accessory muscles (IC) or with the diaphragm, accompanied by outward abdominal motion (Ab). In six additional subjects we inferred the topographical distribution of helium boli during similar breaths and flow rates from the slope of the alveolar plateau recorded during a slow expiration (less than 0.5 l/s). Distribution of the helium boli was studied during natural as well as IC and Ab inspirations. At each of the flow rates IC breaths distributed relatively more of the inspired bolus to upper lung regions than did Ab inspirations. Natural breaths at 0.25 l/s resulted in distributions similar to those of Ab inspirations, whereas at 1.5 l/s the distribution approached that of IC inspirations. A three-compartment model, representing upper, middle, and lower lung regions, was used to simulate bolus distribution. The experimental data showed substantial departure from predictions based on regional time constants alone. However, additional small differences in applied pressure (less than 0.50 cmH2O) between the regions satisfactorily accounted for the gas distribution.

DNP (2,4 dinitrophenol), in concentrations of 2 to 5 x 10 -5 M produced changes in transmembrane action potential in both the Purkinje and ventricular muscle fibers of the isolated perfused hog heart; however, the time of initiation and rate of change of the different phases of the action potential in the two fibers varied. In the Purkinje fiber, the earliest and most pronounced alteration was a loss in overshoot resulting in a decrease in amplitude of the action potential. Shortly thereafter, the action potential duration shortened, and membrane resting potential decreased. In the ventricular muscle fiber, the earliest and most prominent change was a shortening of action potential duration. This was followed by loss in overshoot and decrease in amplitude of action potential. The membrane resting potential declined but was not significantly different from that noted in Purkinje fiber. The changes in both fibers were reversed completely by washing with Tyrode's solution. The earlier and more pronounced shortening of action potential duration in ventricular muscle fiber as compared to Purkinje is attributed to a greater need of the former for metabolic energy. It may also be conjectured that the greater shortening of action potential duration in ventricular fiber is due to a more marked inhibitory effect of K + influx by 2,4 dinitrophenol in this fiber with the K + influx coupled to metabolic energy. To account for the more enhanced loss in overshoot in Purkinje fiber, it is suggested that 2,4 dinitrophenol has a greater modifying effect on Purkinje fiber membrane or on its Na + carrying system. This results in an earlier and more pronounced decrease in Na + influx in this fiber as compared with ventricular muscle fiber.

No abstract

Parachloromercuribenzoate (0.5 to 2.6 x 10–4 m) was administered to a hog Purkinje fiber ventricular muscle preparation and its effects on transmembrane action potentials of the two types of fibers were studied. Parachloromercuribenzoate produced changes in action potential of Purkinje but little change in that of ventricular fiber. The earliest alteration in Purkinje fiber was a decrease in overshoot. This was followed by a decrease in height of action potential and slowing in rate of depolarization. There was a decline in diastolic resting potential but this occurred late. The difference in response of the two types of fibers is not readily explainable. One possible difference is that the sulfhydryl groups in Purkinje fiber may be more available for binding with p-chloromercuribenzoate. Another hypothesis is predicated on differences in metabolism in two types of fibers. There is evidence to indicate that Purkinje fiber utilizes anaerobic glycolysis predominantly. A greater sensitivity of the glycolytic-dependent sulfhydryl enzymes to action of this agent would interfere with metabolism in Purkinje fiber and cause a decrease in its resting potential.