2,4-D-Induced Changes in the K+ Uptake of Wheat Roots at Different pH Values

The effects of an auxin herbicide, 2,4-D, at a concentration of 0.01 mM, on the K⁺ uptake and efflux of excised roots of wheat (Triticum aestivum L. cv. Rannaya) were investigated at different pH values. The K⁺ movement was monitored with a K⁺ (⁸⁶Rb) tracer. In parallel experiments the ATPase activities of microsomal fractions were determined by the inorganic phosphate liberation method. 2,4-D inhibited the K⁺ uptake especially at low pH, irrespective of whether Ca²⁺ was present or not. No marked changes were observed in the K⁺ efflux properties at pH values above 4. The inhibitory effect on K⁺ uptake exhibited a correlation with the hydrocarbon solubility of the herbicide, but not with the 2,4-D-induced decrease of the ATPase activity. It is suggested that 2,4-D exerts a non-specific effect on the lipid-protein interactions, giving rise to a generalized alteration of the transport barrier properties of the plasma membrane even at as low a concentration as 0.01 mM.     

Evaluation of phosphorus in forest soils: Comparison of phosphorus uptake,extraction method and soil properties

Summary Phosphorus in soils from plantation of red pine (Pinus resinosa Ait.) was determined using six extractants: 0.002N H₂SO₄ (pH 3.0); 0.025N HCl+ +0.03N NH₄F; 0.5N NaHCO₃ (pH 8.5);N NH₄OAc (pH 4.8); anion exchange resin (Dower –2, Cl-form); H₂O. Correlations of extractable P with Al- and Al-+Fe-P indicated that these fractions are the dominant forms of inorganic P in most of the soils.Uptake of P by corn and Monterey pine seedlings grown in greenhouse culture was correlated with soil P extracted by the different methods. The most successful of the extractants for predicting P uptake was resin extractable P; the simple correlation coefficients were 0.811 and 0.609 for pine and corn respectively. P uptake by pine correlated significantly with 0.002N H₂SO₄ P (r=0.679),N NH₄OAc P (r=0.443), H₂O P (r=0.549) and Al-+Fe-P (r=0.532) while P uptake by corn correlated with 0.002N H₂SO₄ P (r=0.579), H₂O P (r=0.477) and organic P (r=0.460). Per cent P in pine seedling tops correlated significantly with 0.002N H₂SO₄, resin andN NH₄ OAc extractable P. Multiple regressions which included silt+clay and organic P improved correlations of some soil tests with P uptake in corn and pine seedlings respectively.Research supported by the School of Natural Resources, College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison, the Wisconsin Department of Natural Resources and FAO Fellowship to the senior author.     

The cardiac innervation of Eledone cirrhosa (Lamarck) (Mollusca: Cephalopoda)

The innervation to the cardiac organs and vessels of the octopods Eledone cirrhosa, E. moschata and Octopus vulgaris is described from vitally stained fresh material and wax-embedded sections. This innervation arises from the paired visceral nerves and includes two main peripheral ganglia (fusiform and cardiac) on each side. Several new details of the innervation are reported. Nerves supplying the lateral venae cavae arise from the ventricular nerves at the level of the ventricle. Nerve fibres run to the efferent branchial vessels from the cardiac ganglia. A small ganglion, lying on the auriculo-ventricular nerve, is described for some specimens of both species of Eledone, and is named the auricular ganglion. Commissural strands linking the right and left ventricular nerves of either side are found in Eledone, comparable to those previously described from Octopus. The detailed branching pattern of the innervation shows considerable individual variation and consistent interspecific differences. In E. cirrhosa the fine fibres innervating the inner and outer muscle layers of the auricle show distinct differences in their configuration. Innervation at the surface of the ventricular lumen and around the coronary arterial vessels shows evidence of specialization. The muscle of the branchial heart, particularly the valve leaflets at the junction of the heart and the lateral vena cava, is abundantly innervated. The observations are discussed in relation to other cephalopods and to their probable physiological significance. It is suggested that they provide evidence for a greater degree of neural influence in the control of the cardiac organs than is usually supposed and that they support the idea that the lateral venae cavae have a significant role in the generation of circulatory pressures.     

Cytolytic T lymphocyte responses to metabolically inactivated stimulator cell. I. Metabolic inactivation impairs both CD and LD antigen signals

The effects of metabolic inactivation of spleen cells on antigen presentation to precursors of alloreactive cytolytic T lymphocytes (T_c) were examined. By serological methods, populations inactivated by ultraviolet irradiation, glutaraldehyde fixation or plasma membrane isolation were found to retain normal levels of H-2K/D and Ia antigens. However, comparison of the antigen doses required to stimulate secondary T_c responses in mixed leukocyte culture showed that the inactivated preparations were approximately 10-fold less immunogenic than X-irradiated spleen cells. Their total inability to stimulate primary cytolytic responses pointed to at least a 100-fold impairment of immunogenicity for unprimed T_c precursors in the case of uv-irradiated and glutaraldehyde-treated stimulator cells, and at least a 10-fold impairment for membrane fragments. Experiments showing that the capacity of cell monolayers to absorb precursor T_c from unprimed spleen populations was reduced following uv-irradiation or glutaraldehyde treatment provided direct evidence that this loss of immunogenicity was due in part to suboptimal antigen presentation to precursor T_c. It is concluded that, in addition to the traditional view that these treatments damage the “LD” signal to helper T lymphocytes, metabolic inactivation also impairs recognition of “CD” determinants by precursor T_c.     

Evidence for functional heterogeneity in IgG Fc-binding proteins associated with group A streptococci

A number of group A streptococcal isolates have been compared for their nonimmune reactivity with each human IgG subclass, and rabbit, pig, or horse IgG. The results obtained demonstrate considerable heterogeneity in the expression of type II IgG-binding proteins among and within group A isolates. Extraction and analysis of type II IgG-binding proteins from selected strains demonstrate the existence of five functionally distinct IgG-binding proteins. The type IIo IgG binding protein displayed the greatest range of reactivities, binding to all four human IgG subclasses, and rabbit, pig, and horse IgG. A variant of this protein, designated type II'o, bound all four human subclasses and rabbit IgG, but failed to react with pig or horse IgG. A type IIa protein was recovered from certain group A strains which bound human IgG1, IgG2, IgG4, as well as reacting with rabbit, pig, and horse IgG. A functionally related type IIc activity that displayed all of the reactivities of the type IIa protein but did not bind with human IgG2 was also identified. The final functional form of group A IgG-binding protein, the type IIb protein, bound exclusively to human IgG3. Comparison of these functionally different type II IgG-binding proteins demonstrated no simple structure-function relationship. These studies underscore the heterogeneity of type II Ig-binding proteins expressed by different group A streptococci and document that a single strain can change its pattern of expression of type II IgG-binding protein both quantitatively and qualitatively.     

Vascular smooth muscle cell detachment from elastin and migration through elastic laminae is promoted by chondroitin sulfate-induced “shedding” of the 67-kDa cell surface elastin binding protein

Impaired elastin fiber assembly is observed in the fetal ductus arteriosus (DA), associated with a reduced concentration of elastin binding protein (EBP), a 67-kDa galactolectin. It is also seen in cultured aortic (Ao) smooth muscle cells (SMC) following the release of the EBP by glycosaminoglycans rich in AN-acetylgalactosamine, such as chondroitin sulfate (CS). In the DA, impaired elastin fiber assembly is observed in conjunction with intimal thickening associated with increased migration of SMC into the subendothelium, a feature we previously related to increased production of fibronectin. In this report, we determined whether SMC use the EBP to attach to an elastin substrate, whether shedding of the EBP promotes SMC migration through a threedimensional network of pure elastic laminae prepared from sheep aorta, and whether the latter is associated with increased production of fibronectin. We observed reduced attachment to elastin-coated surfaces of DA SMC deficient in EBP compared to Ao SMC. Addition of CS but not heparan sulfate (a glycosaminoglycan which does not induce EBP shedding) decreased Ao SMC attachment to elastin, as did preincubation with VGVAPG elastin-derived peptides which saturate the EBP. The immunolocalization of cell surface EBP suggested that cells can quickly replace EBP released from their surfaces by CS treatment. The magnitude of CS-induced impaired attachment of SMC to elastin was dose dependent and could be further increased by the administration of cyclohexamide and sodium azide. Also, the reversibility of CS-induced detachment was prevented by monensin. This suggests that a process of new synthesis and intracellular transport of the EBP was necessary to replace the EBP molecules released from the cell surface by CS treatment. In the migration assay, both DA and Ao SMC attached to the top of an elastin membrane, but only DA SMC deficient in EBP migrated through the laminae. Addition of CS, which induced shedding of EBP, resulted in Ao SMC migration associated with increased synthesis of fibronectin. We postulate that CS-induced release of EBP from SMC surfaces causes cell detachment from elastin and an increase in fibronectin synthesis, processes which may be critical in promoting SMC migration associated with intimal thickening developmentally in the DA and perhaps also in vascular disease.     

Two functionally distinct 4-aminopyridine-sensitive outward K+ currents in rat atrial myocytes

In the experiments here, the detailed kinetic properties of the Ca(2+)-independent, depolarization-activated outward currents (Iout) in enzymatically dispersed adult rat atrial myocytes were studied. Although there is only slight attenuation of peak Iout during brief (100 ms) voltage steps, substantial decay is evident during long (10 s) depolarizations. The analyses here reveal that current inactivation is best described by the sum of two exponential components, which we have termed IKf and IKs to denote the fast and slow components, respectively, of Iout decay. At all test potentials, IKf inactivates approximately 20-fold more rapidly than IKs. Neither the decay time constants nor the fraction of Iout remaining at the end of 10-s depolarizations varies over the potential range of 0 to +50 mV, indicating that the rates of inactivation and recovery from inactivation are voltage independent. IKf recovers from inactivation completely, independent of the recovery of IKs, and IKf recovers approximately 20 times faster than IKs. The pharmacological properties of IKf and IKs are similar: both components are sensitive to 4-aminopyridine (1-5 mM) and both are relatively resistant to externally applied tetraethylammonium (50 mM). Taken together, these findings suggest that IKf and IKs correspond to two functionally distinct K+ currents with similar voltage-dependent properties and pharmacologic sensitivities, but with markedly different rates of inactivation and recovery from inactivation. From the experimental data, several gating models were developed in which voltage-independent inactivation is coupled either to channel opening or to the activation of the individual channel subunits. Experimental testing of predictions of these models suggests that voltage-independent inactivation is coupled to activation, and that inactivation of only a single subunit is required to result in functional inactivation of the channels. This model closely approximates the properties of IKf and IKs, as well as the composite outward currents, measured in adult rat atrial myocytes.