FACTORS INFLUENCING THE RESPONSE OF ISOLATED DOGFISH SKIN MELANOPHORES TO MELANOCYTE-STIMULATING HORMONE

¹ Department of Biology Sciences, Northwestern University, Evanston, Illinois 60201
² The Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. The log dose-response curves to standard MSH, bovine -MSH, and synthetic -MSH were obtained for the melanophores of isolated Squalus acanthias skin, using a reflectometric technique.

2. Urea is not required for the response of Squalus melanophores to MSH, further supporting the view that urea is required solely for maintaining the osmotic balance of elasmobranchs.

3. Hypotonic Ringer (1/10 ) produces marked darkening of Squalus skin, indicating that water entry can cause melanin dispersion.

4. Hypertonic Ringer (2 inhibits MSH action on Squalus melanophores indicating that water entry may occur during MSH action.

5. MSH can act on Squalus or Mustelus melanophores in the absence of sodium and lithium: choline, potassium and magnesium are all capable of replacing sodium in the response of Squalus melanophores.

6. MSH action is reduced in a sodium-free sucrose medium; thus there is a cation requirement for MSH action on Squalus melanophores.

7. Either there is no sodium requirement for MSH action on the dogfishes studied, or the specificity of the sodium requirement for sodium in the dogfish is much lower than in the frog.