DEMONSTRATION OF VOLTAGE-DEPENDENT AND TTX-SENSITIVE NA+-CHANNELS IN HUMAN MELANOCYTES

The electrophysiological properties of cultured human melanocytes were investigated using the whole-cell configuration of the patch-clamp technique. Depolarizations to membrane potentials more positive than -30 mV resulted in the rapid development(<1 ms to peak) of an inward current. The maximum peak current was observed at +10 mV and reached an average amplitude of about 270 pA. During the depolarizations, the current inactivated with a time constant of about 2 ms. The current was abolished by the addition of 0.3 mu M tetrodotoxin, a blocker of voltage-gated Na+-channels, and disappeared when Na+ was omitted from the extracellular medium. In addition, the melanocytes contain at least two types of outward K+-current. The first type, observed in every cell, was highly sensitive (K-i 1 mM) to the K+-channel blocker TEA, required depolarizations beyond zero to be activated and did not inactivate. The second type was less regularly observed (10% of the cells). This current activated at more negative voltages (-20 mV), was resistant to TEA (20 mM) but was blocked by 2 mM 4-aminopyridine and inactivated rapidly during depolarizations. We conclude that human melanocytes are equipped with voltage-dependent Na+-channels, a delayed rectifying K+-current and a K+-current similar to the A-current in neurones.