Control of the Amiloride-Sensitive Na+ Current in Salivary Duct Cells by Extracellular Sodium

We have previously reported that intralobular salivary duct cells contain an amiloride-sensitive Na⁺ conductance (probably located in the apical membranes). Since the amiloride-sensitive Na⁺ conductances in other tight epithelia have been reported to be controlled by extracellular (luminal) Na⁺, we decided to use whole-cell patch clamp techniques to investigate whether the Na⁺ conductance in salivary duct cells is also regulated by extracellular Na⁺. Using Na⁺-free pipette solutions, we observed that the whole-cell Na⁺ conductance increased when the extracellular Na⁺ was increased, whereas the whole-cell Na⁺ permeability, as defined in the Goldman equation, decreased. The dependency of the whole-cell Na⁺ conductance on extracellular Na⁺ could be described by the Michaelis-Menten equation with a K _m of 47.3 mmol/1 and a maximum conductance (G _max) of 2.18 nS. To investigate whether this saturation of the Na⁺ conductance with increasing extracellular Na⁺ was due to a reduction in channel activity or to saturation of the single-channel current, we used fluctuation analysis of the noise generated during the onset of blockade of the Na⁺ current with 200 μmol/l 6-chloro-3,5-diaminopyrazine-2-carboxamide. Using this technique, we estimated the single channel conductance to be 4 pS when the channel was bathed symmetrically in 150 mmol/l Na⁺ solutions. We found that Na⁺ channel activity, defined as the open probability multiplied by the number of available channels, did not alter with increasing extracellular Na⁺. On the other hand, the single-channel current saturated with increasing extracellular Na⁺ and, consequently, whole-cell Na⁺ permeability declined. In other words, the decline in Na⁺ permeability in salivary duct cells with increasing extracellular Na⁺ concentration is due simply to saturation of the single-channel Na⁺ conductance rather than to inactivation of channel activity. Received: 27 July 1995/Revised: 7 December 1995     

A single tryptophan on M2 of glutamate receptor channels confers high permeability to divalent cations.

Ionotropic glutamate receptors (iGluRs) of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate subtype display lower permeability to Ca2+ than the N-methyl-D-aspartate (NMDA) subtype. The well-documented N/Q/R site on the M2 transmembrane segment (M2) is an important determinant of the distinct Ca2+ permeability exhibited by members of the non-NMDA receptor subfamily. This site, however, does not completely account for the different permeation properties displayed by non-NMDA and NMDA receptors, suggesting the involvement of other molecular determinants. We have identified additional molecular elements on M2 of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate receptor GluR1 that specify its permeation properties. Higher permeability to divalent over monovalent cations is conferred on GluR1 by a tryptophan at position 577, whereas blockade by external divalent cations is imparted by an asparagine at position 582. Hence, the permeation properties of ionotropic glutamate receptors appear to be primarily specified by two distinct determinants on M2, the well-known N/Q/R site and the newly identified L/W site. These findings substantiate the notion that M2 is a structural component of the pore lining.     

Growth kinetics of Lactobacillus acidophilus under ohmic heating

Lactobacillus acidophilus OSU133 was inoculated into MRS broth in a fermenter vessel and incubated at 30, 35, or 45 degrees C with agitation. Incubation temperatures were attained by conventional or ohmic heating. An electrical current at low (15 V) or high (40 V) voltage was used to heat the culture directly during fermentations under ohmic heating. The growth parameters (lag period, minimum generation time, and maximum growth) and changes in pH were determined during fermentation. Metabolic activities (consumption of glucose and production of lactic acid and bacteriocin) were determined during fermentation at 35 degrees C under both heating methods. Lag period for L. acidophilus was affected appreciably by the method of heating, but the magnitude of these changes depended on the fermentation temperature. When fermentation was done at 30 degrees C, lag period decreased by 94% under low-voltage ohmic, compared with conventional, heating methods. Ohmic heating did not change the generation time significantly and caused slight, but significant (p < 0.01) decrease in maximum growth. Therefore, the electric current enhances the early stages, but it inhibits the late stages of growth. Ohmic, compared with conventional, heating resulted in higher final pH and lower bacteriocin activity in the fermented medium. However, ohmic heating at 35 degrees C had minimal effect on glucose utilization and lactic acid production by L. acidophilus. Results show that measurement of the electric current when ohmic heating is done at a constant voltage may be used in monitoring such fermentations. In conclusion, ohmic heating is potentially useful in certain applications related to fermented foods. (c) 1996 John Wiley & Sons, Inc.     

Evidence for ion chain mechanism of the nonlinear charge transport of hydrophobic ions across lipid bilayers.

The conductivity across a lipid bilayer by tetraphenylborate anion is increased 10-fold on the photoformation of lipophilic porphyrin cations. The cations alone have negligible conductivity. This nonlinear photogenerated increase of ion conductivity is termed the photogating effect. Substitution of H by Cl in the para position of tetraphenylborate leads to a 100-fold enhancement of conductivity, whereas the dark conductivities for this and other substituted borates are the same. Moreover, the halo-substituted borates show a large enhancement of conductivity in the low concentration range (10(-8) M), whereas that of tetraphenylborate is small and space charge is negligible. The enhanced ion conductivity has great structural sensitivity to the structure of the anion, the cation, and the lipid, whereas the partition coefficient of all the borates and the concentration of photoformed cations are only slightly affected. The photogated ion transport has a twofold larger activation energy than transport in the dark. Time-resolved photocurrents and voltages demonstrate that the translocation rate of the porphyrin cation is also enhanced 100-fold by the Cl-borate anion but only 10-fold by the H-borate anion. For these reasons the nonlinear gating effect cannot be explained by electrostatics alone, but requires an ion chain or ion aggregate mechanism. Kinetic modeling of the photoinduced current with a mixed cation-anion ion chain can fit the data well. The photogating effect allows the direct study of ion interactions within the bilayer.     

Floristic diversity and co-occurrences in a subtropical broad-leaved forest and two contrasting regrowth stands in central-west Yunnan Province,China

Many of the natural forested ecosystems that still remain in mainland China are being cleared with potentially detrimental effects on woody plant species diversity on both local and regional scales. The most extensive stand of subtropical broad-leaved forest remaining in China is located in Yunnan Province. In an effort to document the influence of human-induced disturbance on Yunnan's woody flora, floristic inventories were conducted in a stand of primary forest and in regrowth stands located in its interior and along its outer margin in the Xujiaba Nature Sanctuary in the Ailao Mountain Range. Of particular interest was the location of the disturbance relative to the primary forest source area. A total of 134 woody plant species representing 74 genera and 43 families were recorded. The floristics of the two regrowth stands were significantly different from each other, with < 10% of their respective floras comprised of co-occurring species. The interior regrowth stand had a higher number of co-occurring species with the primary forest; however, > 40% were still non-co-occurring.The principal families represented in the primary forest and the interior regrowth stand were Aquifoliaceae, Berberidaceae, Fagaceae, Lauraceae, Rosaceae, Smilacaceae, Symplocaceae, Theaceae, and Vacciniaceae. The three dominant species with relative importance values ranging from > 5% to 18% in both the primary forest and the interior regrowth stand were Castanopsis wattii, Lithocarpus jingdongensis, and Symplocos sumuntia. The edge regrowth stands had the lowest species diversity and were dominated by the native pine Pinus yunnanensis, with a relative importance of 24%. The principal families represented in the edge regrowth stand were Betulaceae, Ericaceae, Fagaceae, Myricaceae, Pinaceae, and Theaceae. Only the Fagaceae and Theaceae were well-represented in all three stands. The results of the study document the low species diversity in post-cutting regrowth on the margins of the primary forest as compared with post-cutting regrowth in the forest interior.     

RAPD typing of clinical isolates of Staphylococcus haemolyticus

The randomly amplified polymorphic DNA (RAPD) assay was used to generate DNA fingerprints from clinical isolates of Staphylococcus haemolyticus isolated from patients treated with continuous ambulatory peritoneal dialysis and previously subjected to a combination of typing methods. The RAPD profiles generated with one of six randomly designed 10-mer primers allowed visual discrimination of strains. Good correlation with the original typing scheme was achieved but RAPD typing allowed discrimination of strains previously indistinguishable.     

Comparison of prevalence of schizophrenia among residents of hostels for homeless people in 1966 and 1992.

OBJECTIVE--To determine whether the prevalence of schizophrenia among the homeless population of Edinburgh resident in hostels has changed between 1966 and 1992. DESIGN--Comparison of two cross sectional surveys. SETTINGS--Hostels for homeless people in Edinburgh. SUBJECTS--In 1966 a random sample of 98 residents of three common lodging houses. In 1992 a random sample of 198 residents of nine hostels. MAIN OUTCOME MEASURE--Prevalence of schizophrenia. RESULTS--The prevalence of schizophrenia in 1992 was 12/136 (9%) compared with 20/79 (25%) in 1966 (odds ratio 0.29; 95% confidence interval 0.13 to 0.62; P = 0.001). Adjustment for confounding by age, current hostel, and duration of unemployment by means of logistic regression produced an adjusted odds ratio of 0.22 (0.08 to 0.58). CONCLUSIONS--The prevalence of schizophrenia was lower in 1992 even after other changes in the population resident in hostels occurring between 1966 and 1992 were taken into account. The findings are not consistent with an increase in the prevalence of schizophrenia among homeless people despite a 66% reduction in adult psychiatric beds in the region during 1966-92.     

Production and initial characterisation of the xylan-degrading system of Phanerochaete chrysosporium

We report the optimum conditions for the degradation of oat spelt arabinoxylan and a preliminary characterisation of the inducible xylan-degrading system of the lignin-degrading white-rot fungus Phanerochaete chrysosporium. Xylanase activity was optimal at pH 5.0 and 50°C; see attached sheet the maximum reaction velocity (V_max) of the system was 3.86 units (U) mg^–1 protein with arabinoxylan as substrate and the substrate concentration giving half V_max (S_0.5) was 0.52 mg ml^–1. At concentrations of arabinoxylan greater than 15 mg ml^–1 excess substrate inhibition was observed. Xylose at 0.9 mm inhibited activity to the extent of 50%. Xylanase activity increased as a function of the dilution of the enzyme preparation prior to assay. It was resolved into four peaks by using a DEAE-Biogel column; the material in these peaks differed with respect to xylan solubilisation and the formation of reducing sugars. Electrofocusing gels allowed visualisation of several bands of activity corresponding to each peak. The arabinoxylan degradation system of P. chrysosporium is therefore composed of multiple components. Correspondence to: P. Broda     

Sterilization of various diameter dead-ended tubes

Effect of tube diameter on steam-in-place sterilization of dead-ended tubes was studied by examining temperature profiles and rates of kill of Bacillus stearothermophilus spores. Time required for sterilization was determined for 9.4-cm-long tubes with various inside diameters from 0.4 to 1.7 cm. Sterilization time increased with decreasing tube diameter. Experimentally measured kill kinetics in 1.7-cm tubes were in agreement with those predicted if measured temperatures represented saturated steam. A 12-log spore reduction was achieved in 1.7-cm diameter vertical and horizontal tubes in less than 63 minutes. For smaller diameter tubes, entrapped air remained after 2 hours and rates of kill were very dependent on position within the tube, tube diameter, and tube orientation with respect to the gravitational vector. Times to achieve a 1-log drop in spore population in the smaller tubes were as much as 10 times greater than those expected if measured temperatures represented saturated steam. Sterilization was not achieved throughout the 0.4-cm tubes. Recommendations are made for including steam bleeders or using prevaccum cycles for these smaller diameter tubes. (c) 1993 John Wiley & Sons, Inc.