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Proton Efflux (proton + efflux)
Selected AbstractsEpidermal growth factor stimulates proton efflux from chondrocytic cellsJOURNAL OF CELLULAR PHYSIOLOGY, Issue 1 2002Kevin E.H. Lui Proton efflux from chondrocytes alters the extracellular pH and ionic composition of cartilage, and influences the synthesis and degradation of extracellular matrix. Epidermal growth factor (EGF) promotes chondrocyte proliferation during skeletal development and accumulates in the synovial fluid in rheumatoid arthritis. The purpose of this study was to investigate the effect of EGF on proton efflux from chondrocytes. When monitored using a Cytosensor microphysiometer, EGF was found to rapidly activate proton efflux from CFK2 chondrocytic cells and rat articular chondrocytes. The actions of EGF were concentration-dependent with half-maximal effects at 0.3,0.7 ng/ml. Partial desensitization and time-dependent recovery of the response were observed following repeated exposures to EGF. EGF-induced proton efflux was dependent on extracellular glucose, and inhibitors of Na+/H+ exchange (NHE) markedly attenuated the initial increase in proton efflux. The response was diminished by inhibitors of phosphatidylinositol 3-kinase and phospholipase C, but not by inhibitors of MEK (MAPK/ERK kinase) or protein kinase A or C. Thus, EGF-induced proton efflux involves glucose metabolism and NHE, and is regulated by a discrete subset of EGF-activated signaling pathways. In vivo, proton efflux induced by EGF may lead to an acidic environment, enhancing turnover of cartilage matrix during development and in rheumatoid arthritis. © 2002 Wiley-Liss, Inc. [source] Functional Complementation of the Yeast P-type H+ -ATPase, PMA1, by the Pneumocystis carinii P-type H+ -ATPase, PCA1THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2006DANIELA GRIGORE ABSTRACT. The opportunistic fungus Pneumocystis is the etiologic agent of an interstitial plasma cell pneumonia that primarily afflicts immunocompromised individuals. Like other fungi Pneumocystis maintains a H+ plasma membrane gradient to drive nutrient uptake and regulates intracellular pH by ATP-dependent proton efflux. Previously, we identified a Pneumocystis gene, PCA1, whose predicted protein product was homologous to fungal proton pumps. In this study, we show by functional complementation in a Saccharomyces strain whose endogenous PMA1 proton pump activity is repressed that the Pneumocystis PCA1 encodes a H+ -ATPase. The properties of PCA1 characterized in this system closely resemble those of yeast PMA1. Yeast expressing PCA1 grow at low pH and are able to acidify the external media. Maximal enzyme activity (Vmax) and efficiency of substrate utilization (Km) in plasma membranes were nearly identical for PCA1 and PMA1. PCA1 contains an inhibitory COOH-terminal domain; removal of the final 40 amino acids significantly increased Vmax and growth at pH 6.5. PCA1 activity was inhibited by proton pump inhibitors omeprazole and lansoprazole, but was unaffected by H+/K+ -ATPase inhibitor SCH28080. Thus, H+ homeostasis in Pneumocystis is likely regulated as in other fungi. This work also establishes a system for screening PCA1 inhibitors to identify new anti- Pneumocystis agents. [source] | ||||||||||