AJP - Endocrinology and Metabolism, Vol 241, Issue 1 84-E89, Copyright © 1981 by American Physiological Society
Localization and characterization of adrenergic receptors on frog skin melanophores
M. A. Longshore and J. M. Horowitz
The functional location of adrenergic binding sites was studied in frog
skin melanophores by injecting norepinephrine (NE) outside and inside a
melanophore. In 49 groups of cells (75% of the fields tested) iontophoretic
injection of NE outside the cell caused melanosome aggregation in the
target cell and/or in the field. In six cells in which a resting membrane
potential was measured before and after intracellular injection (10-90 nA),
NE elicited no change in melanosome configuration. Once the receptors were
localized, the effect of temperature on these receptors was determined by
measuring the reflectance of skins (an indication of melanosome aggregation
or dispersion) in two populations of frogs treated with NE, Rana pipiens
pipiens (with dominant alpha-receptors) and Rana berlandieri forreri (with
dominant beta-receptors). NE (0.1 mM) caused melanosome aggregation in the
former and dispersion in the latter tested at 12, 22, and 40 degrees C. The
iontophoretic and reflectance results suggest that the binding site of the
adrenergic receptor is located on the outer surface of the plasma membrane
of melanophores and that alpha- and beta-receptors evoke aggregation and
dispersion, respectively, within the temperature range of these
experiments.
