The expression of insulin receptor mRNA was examined in rat pancreatic islet cells by single-cell reverse transcriptase (RT)–polymerase chain reaction (PCR). Single cells from disaggregated islets were individually isolated in a microcapillary pipet, and the β-cells were identified by amplification of the mRNA for insulin. We found that in single β-cells, the mRNA for the insulin receptor was also expressed. The fraction of single islet cells expressing both insulin receptor and insulin mRNAs corresponds closely to the fraction of β-cells in the disaggregated islet cell preparation. These results indicate that normal β-cells have the potential to express authentic insulin receptors. Immunohistochemical analysis was insufficiently sensitive for assaying insulin receptor protein; however, insulin receptor substrate 1 (IRS-1) was readily immunolocalized in islet β-cells. Since IRS-1 links several cell surface receptors, including those for insulin and IGF-I, to distal signal transduction pathways, our observations indicate that hormonal regulation of islet β-cells potentially involves the same signal transduction pathway that mediates insulin and growth factor signaling in peripheral insulin target tissue cell types.

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