Short and reversible uncoupling evokes little change in the gap junctions of pancreatic acinar cells

Three different preparations of mouse pancreatic fragments where all the cells tested electrophysiologically showed (a) complete electrical coupling (control), (b) complete uncoupling (after 1-to 2-min exposure to 100% CO2), or (c) complete recoupling (1-2 min after removal of 100% CO2) were fixed, with the electrodes in situ, with 0.2% glutaraldehyde and freeze-fractured for quantitative analysis of acinar cell gap junctions. No obvious difference was observed between gap junctions of coupled and uncoupled acinar cells. However, quantitation revealed a small (2.3-5.6%) increase in particle diameter and spacing within junctions of uncoupled cells. Such increase was rapidly reversed upon cell recoupling. In all preparations, most of the gap junctions were made up of disordered arrays of particles but a few of them showed a more tight packing of their particles of which most had lost the usual globular appearance. These "amorphous" gap junctions had larger particle diameter but smaller particle spacing than the other gap junctions and these parameters were not modified during cell uncoupling. However, "amorphous" gap junctions were more frequent in the latter condition.     

The relationship between sister-chromatid exchange and perturbations in DNA replication in mutant EM9 and normal CHO cells

The majority of the high (12-fold elevated) baseline sister-chromatid exchanges (SCEs) that occur in the CHO mutant line EM9 appear to be a consequence of incorporated BrdUrd, and they arise during replication of DNA containing BrdUrd in a template strand. In normal CHO cells the alkaline elution patterns of DNA newly replicated on a BrdUrd-containing template are significantly altered compared with those seen during the replication on an unsubstituted template. The nascent DNA synthesized on such an altered template is delayed in reaching mature size, possibly because replication forks are temporarily blocked at sites occurring randomly along the template. Transient blockage of replication forks may be a prerequisite for SCE. The delay in replication on BrdUrd-substituted templates was greater in EM9 cells than in parental AA8 cells and was also greater in AA8 cells treated with benzamide, an inhibitor of poly(ADPR) polymerase, than in untreated AA8 cells. Under these conditions, treatment with benzamide also produced a 7-fold increase in SCEs in AA8. An EM9-derived revertant line that has a low baseline SCE frequency showed less delay in replication on BrdUrd-substituted templates than did EM9. However, under conditions where the template strand contained CldUrd, which was shown to produce 4-fold more SCEs than BrdUrd in AA8 cells, the replication delay in AA8 was not any greater in the CldUrd-substituted cells. Thus, other factors besides the delay appear to be involved in the production of SCEs by the template lesions resulting from incorporation of the halogen-substituted pyrimidine molecules.     

The effect of energization on the apparent Michaelis–Menten constant for oxyge in nmitochondrial respiration

Lineweaver-Burk plots of 1/v against 1/[O(2)] for rat liver mitochondrial respiration with succinate or ascorbate+NNN'N'-tetramethyl-p-phenylenediamine as substrates are non-linear. In state 3u (uncoupled by trifluoromethoxycarbonyl cyanide phenylhydrazone) such plots tend to be concave upward, whereas in state 4 (energized) the plots were concave downward. The apparent K(m) for oxygen is larger in state 4 than in state 3u, despite the higher turnover in the latter system. It is postulated that at least one reversible reaction occurs between cytochrome c and cytochrome c oxidase, whose rate is increased on energization (reversed electron transfer); a model including such a reaction is proposed which accounts semiquantitatively for the observations.     

Release of microbial contamination from fractured solids

Estimation of the probability of release of microbial contamination from the interior of solids upon fracture due to impact is essential to the formulation of planetary quarantine and spacecraft sterilization requirements. A model system was designed in which known concentrations of bacterial spores were incorporated in methyl methacrylate plastic. Pieces of plastic were fractured in a uniform manner exposing interior surface areas of consistent and measurable size. Known surface areas were incubated in sets of 20 culture tubes containing liquid growth medium. The subsequent occurrence of visible growth expressed as percent of tubes positive was interpreted as an estimate of the probability of release of at least one viable micro-organism.From these experiments probability of release as a function of microbial concentration in plastic was estimated for exposed interior surface areas of 30.6, 61.2, 91.8 or 122.4 mm². Good agreement of the empirical results with a theoretical mathematical model of the probability of release of contamination from solids was demonstrated. Analysis of the data using the maximum likelihood procedure provided a means of calculating a proportionality constant representing the effective thickness of the exposed area and the characteristics of the recovery procedure.     

Das piezoelektrische Verhalten der menschlichen Zahnhartgewebe

Zusammenfassung Bei menschlichen Zähnen wurde piezoelektrisches Verhalten festgestellt; dieses ist gebunden an den Kollagenfaseranteil des Dentins und des Zahnzementes. Schmelz ist nicht piezoelektrisch; entmineralisierte Zähne zeigen ein verstärktes piezoelektrisches Verhalten.Es besteht eine piezoelektrische Achse in der physiologischen Zahnlängsrichtung, deren Richtungssinn bei allen Zähnen des Ober- und Unterkiefers gleich ist und offenbar der morphogenetischen Entwicklungsrichtung des Zahnes entspricht. Außerdem besteht rund um die piezoelektrische Längsachse herum in allen radialen Richtungen zwischen Pulpahöhle und Zahnaußenseite piezoelektrisches Verhalten, das möglicherweise in Beziehung zur Struktur der Dentinlamellen und damit zur morphogenetischen Zahnentwicklung in radialer Richtung steht.Die piezoelektrischen Effekte zeigen von Zahn zu Zahn eine erhebliche biologische Streubreite. Bei unserem Untersuchungsmaterial lagen die Effekte zwischen 3,5·10^–10 und 1,9·10^–9 est E Ldg./dyn. Diese Werte entsprechen etwa 0,5 bis 2,8% des piezoelektrischen Koeffizienten d₁₁ von -Quarz.

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Summary Human teeth are piezoelectric. This is due to the collagen-fibril content of the dentine and tooth cement. Enamel is not piezoelectric; decalcified teeth show increased piezoelectric behaviour.There is a piezoelectrical axis corresponding to the physiological longitudinal tooth axis, which is in the same direction in all teeth of both upper and lower jaws, and which seems to correspond to the morphogenetical development axis of teeth. Piezoelectric behaviour also exists between the pulp cavity and outer surface of the tooth in all directions radial to the piezoelectric longitudinal axis. The latter is possibly due to the dentine lamellae, and therefore may be connected with the radial direction of morphogenetical tooth development.The piezoelectric effects show large biological variations in different teeth. The effects from our research materials vary between 3.5·10^–10 and 1.9·10^–9 e.s.u./dynes. These results correspond to about 0.5 to 2.8% of the piezoelectrical coefficient d₁₁ of -quartz.

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Unterstützt durch Sachbeihilfen der Deutschen Forschungsgemeinschaft.

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cand. med. dent. und derzeit Doktorand an der Klinik und Poliklinik für Zahn-, Mund- und Kieferkrankheiten, Universität Kiel.     

Inositol 1,3,4,5-tetrakisphosphate is essential for sustained activation of the Ca2+-dependent K+ current in single internally perfused mouse lacrimal acinar cells

Summary We have examined the effects of various inositol polyphosphates, alone and in combination, on the Ca²⁺-activated K⁺ current in internally perfused, single mouse lacrimal acinar cells. We used the patch-clamp technique for whole-cell current recording with a set-up allowing exchange of the pipette solution during individual experiments so that control and test periods could be directly compared in individual cells. Inositol 1,4,5-trisphosphate (Ins 1,4,5 P₃) (10–100 m) evoked a transient increase in the Ca²⁺-sensitive K⁺ current that was independent of the presence of Ca²⁺ in the external solution. The transient nature of the Ins 1,4,5 P₃ effect was not due to rapid metabolic breakdown, as similar responses were obtained in the presence of 5mm 2,3-diphosphoglyceric acid, that blocks the hydrolysis of Ins 1,4,5 P₃, as well as with the stable analoguedl-inositol 1,4,5-trisphosphorothioate (Ins 1,4,5 P(S)₃) (100 m). Ins 1,3,4 P₃ (50 m) had no effect, whereas 50 m Ins 2,4,5 P₃ evoked responses similar to those obtained by 10 m Ins 1,4,5 P₃. A sustained increase in Ca²⁺-dependent K⁺ current was only observed when inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5 P₄) (10 m) was added to the Ins 1,4,5 P₃ (10 m)-containing solution and this effect could be terminated by removal of external Ca²⁺. The effect of Ins 1,3,4,5 P₄ was specifically dependent on the presence of Ins 1,4,5 P₃ as it was not found when 10 m concentrations of Ins 1,3,4 P₃ or Ins 2,4,5 P₃ were used. Ins 2,4,5 P₃ (but not Ins 1,3,4 P₃) at the higher concentration of 50 m did, however, support the Ins 1,3,4,5 P₄-evoked sustained current activation. Ins 1,3,4 P₃ could not evoke sustained responses in combination with Ins 1,4,5 P₃ excluding the possibility that the action of Ins 1,3,4,5 P₄ could be mediated by its breakdown product Ins 1,3,4 P₃. Ins 1,3,4,5 P₄ also evoked a sustained response when added to an Ins 1,4,5 P(S)₃-containing solution. Ins 1,3,4,5,6 P₅ (50 m) did not evoke any effect when administered on top of Ins 1,4,5 P₃. In the absence of external Ca²⁺, addition of Ins 1,3,4,5 P₄ to an Ins 1,4,5 P₃-containing internal solution evoked a second transient K⁺ current activation. Readmitting external Ca²⁺ in the continued presence internally of Ins 1,4,5 P₃ and Ins 1,3,4,5 P₄ made the response reappear. We conclude that both Ins 1,4,5 P₃ and Ins 1,3,4,5 P₄ play crucial and specific roles in controlling intracellular Ca²⁺ homeostasis.