GABA from putrescine is bound in macromolecular form in keratinocytes

We report for the first time that the neurotransmitter gamma-aminobutyric acid (GABA) exists in macromolecular form in keratinocytes. GABA derived from putrescine (Pu) has been identified as a component of acid-precipitable material of cultured human keratinocytes. Confluent, stratified cultures of human foreskin keratinocytes exposed to [3H]-Pu for 4 hours took up about 14% of the radioactivity from the medium and 1% of the total cell-associated radioactivity was precipitable by trichloroacetic acid (TCA). Both attached and shed cells were examined by HPLC for Pu and its radioactive metabolites in TCA-insoluble and TCA-soluble fractions. GABA accounted for the major portion (54%) of the radioactivity derived from Pu in the TCA-precipitable material of attached keratinocytes. Pu and spermidine represented lesser amounts, 35% and 9% respectively, of the total TCA-precipitable radioactivity. In addition, a large portion of acid soluble radioactivity derived from Pu (63%) was GABA, whereas Pu and spermidine represented 29% and 6% respectively of the total TCA-soluble radioactivity. The exact origin of GABA in acid-precipitable material, as well as its form of attachment, is currently under investigation.