TRPM4 and melanoma: All variant cell lines tested were positive for mRNAs encoding other subtypes of Trpm, except for Trpm4b, Trpm6, and Trpm8. Although levels of Trpm3a and Trpm4a mRNAs were higher at acidic than at neutral pHe, these levels did not correlate with the metastatic ability of B16 melanoma variants (data not shown).