Samuelson A C, Stockert R J, Novikoff A B, Novikoff P M, Saez J C, Spray D C, Wolkoff A W
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Am J Physiol. 1988 Jun;254(6 Pt 1):C829-38. doi: 10.1152/ajpcell.1988.254.6.C829.
Inhibitors of specific steps in the endocytosis of galactose-terminating glycoproteins (asialoglycoproteins) by cultured rat hepatocytes have been described (J. Cell Biol. 98: 375-381, 1984). In particular, substitution of K+ for Na+ in the culture medium results in reduced delivery of ligand to lysosomes; ligand-receptor internalization, dissociation, and segregation remain normal. We have now demonstrated by direct microelectrode measurement that incubation of hepatocytes in K+-substituted medium results in a reduction of intracellular pH by greater than or equal to 0.5 U. In addition, we have shown that reduced intracellular pH in these cells produced by either direct (CO2 diffusion) or indirect (K+ substitution) acidification inhibits ligand delivery to lysosomes. Return of internalized ligand-receptor complex to the cell surface (diacytosis) is also inhibited by these manipulations. These studies suggest that intracellular pH may modulate specific steps involving vesicle translocation and fusion in the receptor-mediated endocytosis of asialoglycoproteins. Similar effects of direct acidification of hepatocytes by CO2 diffusion and indirect acidification by K+ substitution for Na+, on diacytosis and ligand delivery to lysosomes, suggest that K+ substitution may influence these events by altering intracellular pH.
已有文献报道了培养的大鼠肝细胞对半乳糖末端糖蛋白（去唾液酸糖蛋白）内吞作用中特定步骤的抑制剂（《细胞生物学杂志》98: 375 - 381, 1984）。特别是，在培养基中用K⁺替代Na⁺会导致配体向溶酶体的递送减少；配体 - 受体的内化、解离和分离仍保持正常。我们现在通过直接微电极测量证明，将肝细胞置于K⁺替代培养基中孵育会导致细胞内pH降低大于或等于0.5个单位。此外，我们还表明，通过直接（CO₂扩散）或间接（K⁺替代）酸化使这些细胞内pH降低会抑制配体向溶酶体的递送。这些操作也会抑制内化的配体 - 受体复合物返回细胞表面（再胞吐作用）。这些研究表明，细胞内pH可能调节去唾液酸糖蛋白受体介导的内吞作用中涉及囊泡转运和融合的特定步骤。通过CO₂扩散直接酸化肝细胞以及用K⁺替代Na⁺进行间接酸化，对再胞吐作用和配体向溶酶体的递送具有相似的影响，这表明K⁺替代可能通过改变细胞内pH来影响这些事件。
