engleski

Immunodetection of Na+-D-glucose cotransporters hSGLT1 and hSGLT2 in human organs

A high affinity/low capacity SGLT1 (SLC5A1) and a low affinity/high capacity SGLT2 (SLC5A2) have been identified as the major mediators of Na+-dependent hexose reabsorption in the mammalian nephron. The human transporters exhibit 59% homology and some functional and localizational differences. hSGLT1 transports equally galactose and glucose, and has been localized to the brush-border membrane (BBM) of renal proximal tubules (PT) and small intestine (SI), while hSGLT2 transports glucose much better, and has been detected only in PT. Due to lack of specific antibodies, a detailed immunolocalization of hSGLT1 and hSGLT2 in the human kidney (K) and other organs has not been performed. In this work we used novel polyclonal antibodies against both transporters, and studied their expression in K, SI (jejunum), and liver (L) in humans of both sexes by Western blotting (WB) in isolated total cell membranes (TCM) and by immunocytochemistry (IC) in tissue cryosections. In WB, the hSGLT1-protein band (Mr ~75 kDa) was detected in both K and SI, whereas the hSGLT2-protein band with similar Mr was detected only in K. The studies in TCM from the K cortex (C) and outer stripe (OS) revealed strong zonal (hSGLT1: C<OS ; hSGLT2: C>OS) but no gender differences in their expression. By IC in K, hSGLT1 was restricted to the BBM of S3, while hSGLT2 was localized to the BBM of S1 and S2 segments of PT. In SI, hSGLT1-antibody labeled the ~80 kDa protein band, and stained: a) BBM and subapical vesicles in absorptive cells, and b) apical domain in crypts, with similar intensity in both sexes. In L, hSGLT1-positive was the apical domain of bile ducts. hSGLT2 was absent from both SI and L. Our data indicate that in humans, SGLT2 may serve the Na+-gradient-driven sugar reabsorption exclusively in the convoluted segments of PT in K, whereas SGLT1 may mediate sugar absorption in SI and reabsorption in the straight segment of PT in K and in bile ducts in L.

immunolocalization; nephron; proximal tubule; sex differences

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