We previously reported that hypotonic stress stimulated transepithelial Na⁺ transport via a PTK-dependent pathway. However, it is still unknown what type of PTK mediates this stimulation. In the present study, we investigated the role of receptor tyrosine kinase (RTK) in the hypotonic stimulation of Na⁺ transport. In renal epithelial A6 cells, we observed inhibitory effects of AG1478 (an EGF receptor (EGFR) inhibitor) and AG1296 (an PDGF receptor (PDGFR) inhibitor) on both the hypotonic stress-induced stimulation of Na⁺ transport and the hypotonic stress-induced ligand-independent activation of EGFR. We further studied if hypotonic stress activates MAP kinase family members, ERK1/2, p38 MAPK, and JNK/SAPK, via an RTK-dependent pathway. The present study indicates that hypotonic stress induced phosphorylation of ERK1/2 and JNK/SAPK, but not p38 MAPK, that the hypotonic stress-induced phosphorylation of ERK1/2 and JNK/SAPK was diminished by co-application of AG1478 and AG1296, and that only JNK/SAPK was involved in the hypotonic stimulation of Na⁺ transport. A further study using cyclohexamide suggests that both RTK and JNK/SAPK contributed to the protein synthesis-independent early phase in the hypotonic stress-induced Na⁺ transport, but not to the protein synthesis-dependent late phase. The present study also suggests involvement of phosphatidylinositol 3-kinase (PI3-kinase) in the RTK-JNK/SAPK cascade-mediated Na⁺ transport. These observations indicate that: 1) hypotonic stress activates JNK/SAPK via RTK in a ligand-independent pathway, 2) the RTK-JNK/SAPK cascade acts as a mediator of the hypotonic stress for stimulation of Na⁺ transport, and 3) PI3-kinase is involved in the RTK-JNK/SAPK cascade for the hypotonic stress-induced stimulation of Na⁺ transport.