Cross-talk between insulin and IGF-1 receptors in the cortical collecting duct principal cells: Implication for ENaC-mediated NA⁺ reabsorption

Insulin and IGF-1 are recognized as powerful regulators of the epithelial Na⁺ channel (ENaC) in the aldosterone-sensitive distal nephron. As previously described, these hormones both acutely increase ENaC activity in freshly isolated split open tubules and cultured principal cortical collecting duct cells. The present study was aimed at differentiating the effects of insulin and IGF-1 on Na⁺ transport in immortalized mpkCCD_cl4 cells and defining their interrelations. We have shown that both insulin and IGF-1 applied basolaterally, but not apically, enhanced transepithelial Na⁺ transport in the mpkCCD_cl4 cell line with EC₅₀ values of 8.8 and 14.5 nM, respectively. Insulin treatment evoked phosphorylation of both insulin and IGF-1 receptors, whereas the effects of IGF-1 were more profound on its own receptor rather than the insulin receptor. AG-1024 and PPP, inhibitors of IGF-1 and insulin receptor tyrosine kinase activity, diminished insulin- and IGF-1-stimulated Na⁺ transport in mpkCCD_cl4 cells. The effects of insulin and IGF-1 on ENaC-mediated currents were found to be additive, with insulin likely stimulating both IGF-1 and insulin receptors.