Keratinocytes: a source of the transmitter L-glutamate in the epidermis

Various glutamate receptors have been described in both keratinocytes and melanocytes. L-Glutamate is the physiological agonist of the glutamate receptor family. The source of this transmitter had not yet been identified. In normal human epidermal keratinocytes (NHEK) and HaCaT-keratinocytes, cell supernatants were sampled in various stages of cell density and the l-glutamate content photometrically determined. The following examination time-points were defined: non-confluent (ca. 33%), subconfluent (ca. 70%) and confluent (90-100%). The L-glutamate concentration originally in the culture medium was 14.7 mg/l (0.1 mm/l). The L-glutamate concentration in the cell supernatant increased in NHEK with increasing cell density: non-confluent 39.9 + or - 4 mg/l, subconfluent 60.6 + or - 15.8 mg/l, confluent 100.7 + or - 33.2 mg/l. A linear increase of L-glutamate concentration was also found for HaCaT cells. The investigations show that keratinocytes are capable of producing and releasing L-glutamate. Thus they are a source of L-glutamate which acts as a transmitter on epidermal glutamate receptors.