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Lactate and pH change in close correlation in the extracellular space of the rat brain during cortical spreading depression.

pH sensitive microcelectrodes were used in combination with microdialysis (MD) technique to measure extracellular pH (pHe) and extracellular lactate (lace) within the cortex of rat brains during cortical spreading depression (SD). SD was induced by local K(+)-application and identified by DC recordings. It was accompanied by an extracellular acidification of 0.34 +/- 0.06 pH units and by a 2.8 +/- 0.80 fold increase of lace; the recovery of pHe took place within three phases, that of lace within 2 phases. The recovery of both parameters was complete about 45 min after the onset of SD. We conclude that the changes of lace and pHe are closely related. This indicates both lactate and protons to be transported in parallel.

Animals↗

Trafficking of sulfated glycoprotein-1 (prosaposin) to lysosomes or to the extracellular space in rat Sertoli cells.

Sulfated glycoprotein-1 (prosaposin) exists in 2 forms: a 65kDa form targeted to lysosomes and a 70kDa form secreted extracellularly. In order to understand the sorting and targeting mechanisms of the two forms of SGP-1, we have compared their maturation, processing, and secretion in rat Sertoli cells in vivo. Metabolic labeling experiments in vivo demonstrated that the 65kDa form is synthesized first, then post-translationally modified to the 70kDa form of SGP-1. Subcellular fractionation of testicular homogenate was used to obtain Golgi fractions containing up to 50-fold enrichment in galactosyltransferase. Permeabilization of enriched Golgi fractions with saponin released the 70kDa form, but did not affect the 65kDa protein. While excess free mannose 6-phosphate did not release lysosomal SGP-1, it released the 35kDa cathepsin L from Golgi membranes. Using quantitative electron-microscopic immunocytochemistry, the lysosomal contents of SGP-1 were shown to increase significantly after the administration of tunicamycin in vivo. Therefore, the trafficking of the 65kDa form of SGP-1 to the lysosomes appears to be independent of the M6P-receptor pathway. The 70kDa form of SGP-1 was found to aggregate within perforated Golgi fractions in a process which depends on low pH and calcium ions. We conclude that the targeting of the 65kDa form of SGP-1 to the lysosomes involves an early association with Golgi membrane that is independent of mannose 6-phosphate receptors.

Acid Phosphatase↗