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 ± 4 mg/l, subconfluent 60.6 ± 15.8 mg/l, confluent 100.7 ± 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.