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 microM 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 (Ki 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.
Ekmehag
B
B
Department of Dermatology, University of Lund, Sweden.
Persson
B
B
Rorsman
P
P
Rorsman
H
H
D015761:4-Aminopyridine / Q000494:pharmacology; D004553:Electric Conductivity; D006801:Humans; D008297:Male; D008544:Melanocytes / Q000502:physiology*; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000494:pharmacology; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology*
D015221:Potassium Channels; D015222:Sodium Channels; D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D019789:Tetraethylammonium; D012964:Sodium; D015761:4-Aminopyridine