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1. Intracellular recordings, in conjunction with fura-2 fluorescence imaging, were used to evaluate the contribution of the different Ca2+ channel subtypes to the Ca2+ influx induced by back-propagating trains of action potentials. High-threshold channels contributed mainly to Ca2+ influx in pyramidal cell somata and proximal dendrites, whereas low-threshold and other Ni(2+)-sensitive channels played a greater role in more distal dendritic signaling. These data suggest that the different Ca2+ channel types participate in distinct physiological functions; low-threshold channels likely play a greater role in dendritic integration, whereas high-threshold channels are more important for somatic Ca(2+)-dependent processes.

Background: Bacterial transfer-messenger RNA (tmRNA, 10Sa RNA) is involved in a trans-translation reaction which contributes to the degradation of incompletely synthesized peptides and to the recycling of stalled ribosomes. However, its physiological role in the cell remains elusive. In this study, an ef®cient system for controlling the expression of the gene for tmRNA (ssrA), as well as a tmRNA gene-defective strain (ssrA::cat), were constructed in Bacillus subtilis. The effects of tmRNA on the growth of the cells were investigated under various physiological culture conditions using these strains.

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We have isolated and characterized a novel member (CAT3) of the cationic amino acid transporter (CAT) family. In oocyte injection assays, CAT3 cRNA exhibited a saturable, sodium ion-independent transport activity with high affinity for L-arginine and L-lysine (K m ‫؍‬ 40 -60 and 115-165 M, respectively). Transport of L-arginine was effectively competed only by cationic amino acids in L-form: arginine, lysine, ornithine, and 2,4-diamino-n-butyric acid but not by 2,3-diaminopropionic acid. The presence of L-arginine in the incubation medium stimulated the efflux rate of L-arginine, indicating that CAT3 is subject to trans-stimulation. All these results are consistent with the idea that CAT3, along with CAT1 and CAT2, constitutes the transport activity originally assigned to system y ؉ . Like CAT2, but unlike CAT1, the expression of CAT3 is regulated in a highly tissue-specific manner; when various adult tissues were examined, significant levels of CAT3 transcript were detectable only in brain. In situ hybridization on brain sections revealed that CAT3 transcripts were localized predominantly along the midbrain-thalamus-hypothalamus axis, whereas neither CAT1 nor CAT2 transcripts demonstrated a similar localization. In contrast to its highly localized expression during the primitive streak stage and in the adult stage, CAT3 expression was detected more widely in 13.5 day post-coitum mouse embryos.

Mast cells are widely distributed in the connective tissue of the body, but are particularly prominent in tissues such as skin. An increased number of mast cells can be found in the dermis under inflammatory conditions and ultraviolet (UV) exposed skin. Previous investigations have identified matrix metalloproteinases (MMPs) as key enzymes in the degradation of extra cellular matrix (ECM). This study reports about the potential contribution of human mast cell tryptase as a new triggering enzyme in matrix degradation process. Recent studies suggest that mast cell-derived proteases can activate MMPs. We investigated both the degradation of cellular matrix components and activation of MMPs by human tryptase. Mast cells are increased in photoaged skin and the increase of mast cell tryptase in UV irradiated skin was confirmed. Human mast cell tryptase was purified from human tonsils by a series of standard chromatographic procedures. Degradation of collagen type I was achieved by incubation of human type I collagen with tryptase and the fragments were quantified by SDS-PAGE and staining with Coomassie Brilliant Blue 250-R (CBB). Treatment with tryptase resulted in the activation of proMMP-9 as revealed by gelatinolytic activity in type IV collagen zymography. When tryptase was incubated with human type IV collagen, gradual degradation of intact collagen was detected by Western blotting. Furthermore, type IV collagen degradation was observed in the basement membrane (BM) of a three-dimensional (3D) skin model. Degranulation of mast cells, which release tryptase, can activate MMPs and causes direct damage to ECM proteins. These findings strongly implicate that tryptase either alone or in conjunction with activation of MMPs, can participate in ECM damage and the possible destruction of BM leading to photoaging.