Segment-specific expression of messenger RNA encoding for a glutamate transporter by renal tubule cells

Transport of the amino acid glutamate across plasma membranes of neurons, glial cells and epithelial cells of the small intestine and kidney is carried out via specific transport proteins. Recently, a high-affinity Na(+)-dependent glutamate transporter was cloned from rabbit small intestine. We have designed oligonucleotide probes to sequences of rabbit glutamate transporter mRNA and used these for in situ hybridization histochemistry in order to define the cellular localization of glutamate transporter mRNA in the rabbit kidney. Strong hybridization with the probes to glutamate transporter mRNA was demonstrated in the outer stripe of the outer medulla, with tubular rays radiating into the cortex. In emulsion-dipped and hematoxylin-eosin counterstained sections, it could be seen that cells expressing glutamate transporter mRNA were localized in the outer stripe of the outer medulla, coinciding with the S3 segment of proximal tubules. The results show that glutamate transporter mRNA is expressed in proximal tubule cells of the rabbit kidney, suggesting that Na(+)-dependent uptake of glutamate occurs primarily within this nephron segment.