A note on transmembrane potential in dermal melanophores of the frog and movement of melanin granules.

1. Transmembrane potentials were measured and distribution of melanin granules observed in dermal melanophores of the isolated frog's web.2. In normal Ringer solution, melanin granules were aggregated in the cell bodies and the transmembrane potentials were usually in the range 70-90 mV.3. Addition of alpha-melanocyte stimulating hormone (alpha-MSH) to the bathing solution resulted in dispersion of the melanin granules into the processes of the cells, without any accompanying change in membrane potentials. Altering the membrane potentials by changing the external K(+) concentration had no effect on melanin migration.4. It is concluded that migration of melanin granules in these cells is unrelated to cell membrane polarization.