POU2F1 and diabetes mellitus: There are at least five other organic cation transporters OCTN1, OCTN2, OCT1, OCT2 and OCT3, that have been characterized for functional roles in the uptake of various substrates that include L-carnitine, choline, ergothioneine, and the diabetes and anticancer drugs, metformin and imatinib, respectively [30, 31][32–34].