Inhomogeneity during deflation of excised canine lungs. I. Alveolar pressures

Factors both intrinsic and extrinsic to the lung may cause inhomogeneity of alveolar pressures during deflation. Wilson et al. (J. Appl. Physiol. 59: 1924-1928, 1985) predicted that any such inhomogeneity would be limited by interdependence of regional expiratory flows. To test this hypothesis and to explore how the pleural pressure gradient might affect inhomogeneity of alveolar pressures, we deflated at submaximal flows excised canine lobes that first were suspended in air and then were immersed in foams that simulated the vertical gradient of pleural pressure. Interregional inhomogeneity of regional transpulmonary pressures was measured with use of an alveolar capsule technique. Flow-dependent inhomogeneity of alveolar pressures was present, with differences in alveolar pressure quickly relaxing to a constant limiting value at each flow. Foam immersion increased inhomogeneity at a given flow. We conclude that factors intrinsic to the lung cause significant inhomogeneity of alveolar pressures at submaximal expiratory flows and that this inhomogeneity is enhanced by the extrinsic gradient of pleural pressure. These observations are consistent with the interdependence of flow proposed by Wilson et al.     

Biochemical characterization of a spearmint mutant that resembles peppermint in monoterpene content

A radiation-induced mutant of Scotch spearmint (Mentha × gracilis) was shown to produce an essential oil containing principally C3-oxygenated p-menthane monoterpenes that are typical of peppermint, instead of the C6-oxygenated monoterpene family characteristic of spearmint. In vitro measurement of all of the enzymes responsible for the production of both the C3-oxygenated and C6-oxygenated families of monoterpenes from the common precursor (−)-limonene indicated that a virtually identical complement of enzymes was present in wild type and mutant, with the exception of the microsomal, cytochrome P-450-dependent (−)-limonene hydroxylase; the C6-hydroxylase producing (−)-trans-carveol in the wild type had been replaced by a C3-hydroxylase producing (−)-trans-isopiperitenol in the mutant. Additionally, the mutant, but not the wild type, could carry out the cytochrome P-450-dependent epoxidation of the α,β-unsaturated bond of the ketones formed via C3-hydroxylation. Although present in the wild type, the enzymes of the C3-pathway that convert trans-isopiperitenol to menthol isomers are synthetically inactive because of the absence of the key C3-oxygenated intermediate generated by hydroxylation of limonene. These results, which clarify the origins of the C3- and C6-oxygenation patterns, also allow correction of a number of earlier biogenetic proposals for the formation of monoterpenes in Mentha.     

Sequence of events during Bacillus megaterim spore germination

Levinson, Hillel S. (U.S. Army Natick Laboratories, Natick, Mass.), and Mildred T. Hyatt. Sequence of events during Bacillus megaterium spore germination. J. Bacteriol. 91:1811-1818. 1966.-An integrated investigation of the sequence of events during the germination of Bacillus megaterium spores produced on three different media-Liver "B" (LB), synthetic, and Arret and Kirshbaum (A-K)-is reported. Heat-activated spores were germinated in a mixture of glucose and l-alanine. For studies of dipicolinic acid (DPA) release and increase in stainability and phase-darkening, germination levels were stabilized by the addition of 2 mm HgCl(2). Heat resistance was measured by conventional plating techniques and by a new microscopic method. The sequence (50% completion time) of LB spore germination events was: loss of resistance to heat and to toxic chemicals (3.0 min); DPA loss (4.7 min); stainability and Klett-measured loss of turbidity (5.5 min); phase-darkening (7.0 min); and Beckman DU-measured loss of turbidity (7.2 min). The time difference between 50% completion of stainability and complete phase darkening was 1.5 min, in excellent agreement with the microgermination time of 1.49 min as determined by observation of spores darkening under phase optics. Alteration of the sporulation medium modified the 50% completion times of these germination events, and, in some cases, their sequence. In the A-K spores, the rates of loss of heat resistance and DPA were substantially higher than those of the other germination events, whereas in spores produced in the LB and synthetic media all germination events followed an approximately parallel time course. This is discussed from the point of view of spore population heterogeneity and germination mechanisms.     

Effects of low-chloride solutions on action potentials of sheep cadiac purkinje fibers

The rapid repolarization during phase 1 of the action potential of sheep cardiac purkinje fibers has been attributed to a time- and voltage-dependent chloride current. In part, this conclusion was based on experiments that showed a substantial slowing of phase 1 when larger, presumably impermeant, anions were substituted for chloride in tyrode’s solution. We have re- examined the electrical effects of low-chloride solutions. We recorded action potentials of sheep cardiac purkinje fibers in normal tyrode’s solution and in low-chloride solutions made by substituting sodium propionate, acetylglycinate, methylsulfate, or methanesulfonate for the NaCl of Tyrode’s solution. Total calcium was adjusted to keep calcium ion activity of test solutions equal to that of control solutions. Propionate gave qualitatively variable results in preliminary experiments; it was not tested further. Low-chloride solutions made with the other anions gave much more consistent results: phase 1 and the notch that often occurs between phases 1 and 2 were usually unaffected, and the action potential duration usually increased. The only apparent change in the resting potential was a transient 3-6 mV depolarization when low-chloride solution was first admitted to the chamber, and a symmetrical transient hyperpolarization when chloride was returned to normal. If a time- and voltage-dependent chloride current exists in sheep cardiac purkinje fibers, our results suggest that it plays little role in generating phase 1 of the action potential.