Adrenaline induces hyperpolarization in frog pituitary melanotrophs through activation of potassium channels.
A patch-clamp study was conducted on cultured frog pituitary melanotrophs, in order to investigate the effects of adrenaline on the electrical activity of these cells. In the whole-cell configuration, adrenaline (1 microM) caused hyperpolarization that was accompanied by a fall in membrane input resistance and a blockage of spontaneous action potentials. Under voltage clamp, adrenaline elicited a net-outward current. The hyperpolarization became undetectable at a command voltage of -100 mV which corresponded to the equilibrium potential of potassium ions. The effect of adrenaline on membrane potential and spontaneous activity was blocked by the alpha 2-adrenergic receptor antagonist yohimbine (1-10 microM) but could not be mimicked by the alpha 2-adrenergic agonist clonidine (1-10 microM). In the cell-attached configuration, exposure of the extra-patch membrane to adrenaline increased the occurrence of single-channel currents with a slope conductance of 100 pS. The deduced reversal potential of these currents corresponded to the equilibrium potential of potassium ions. These results suggest that frog melanotrophs display an alpha 2-adrenergic receptor subtype coupled to potassium channels involved in hyperpolarization.
Valentijn
J A
JA
European Institute for Peptide Research, CNRS URA 650, UA INSERM, University of Rouen, Mont-Saint-Aignan, France.
Vaudry
H
H
Cazin
L
L
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D004594:Electrophysiology; D004837:Epinephrine / Q000494:pharmacology*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011895:Rana ridibunda; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D015221:Potassium Channels; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009074:Melanocyte-Stimulating Hormones; D004837:Epinephrine