Role of calcium in thyrotrophin-releasing hormone-stimulated release of melanocyte-stimulating hormone from frog neurointermediate lobe.
The effect of modifications of extracellular calcium concentrations on alpha-MSH release has been studied using perifused frog neurointermediate lobes. Increasing concentrations of calcium (from 2 to 10 mmol/l) gave rise to a dose-related stimulation of alpha-MSH secretion, whereas reduction of Ca2+ from 2 to 1.5 mmol/l partially inhibited alpha-MSH release. The direct effect of extracellular Ca2+ on alpha-MSH secretion was confirmed by the dose-dependent stimulation of alpha-MSH release induced by the calcium ionophore A23187. Perifusion with a calcium-free medium or blockade of Ca2+ channels by 4 mmol Co2+/l both resulted in an inhibition of spontaneous and TRH-induced alpha-MSH release. Conversely, administration of verapamil or methoxyverapamil (10 mumol/l each) did not alter basal secretion and had no effect on the response of the glands to TRH. Nifedipine (10 mumol/l), which was able to block KCl (20 mmol/l)-evoked alpha-MSH release, induced a slight inhibition of basal alpha-MSH secretion, indicating that extracellular Ca2+ levels may regulate alpha-MSH release in part by Ca2+ influx through voltage-dependent Ca2+ channels. In contrast TRH-induced alpha-MSH release was not affected by nifedipine or dantrolene (10 mumol/l), and BAY-K-8644 (1 mumol/l) did not significantly modify the response of neurointermediate lobes to TRH. Taken together, these results suggest that TRH-induced alpha-MSH secretion is associated with calcium influx across the plasma membrane and that calcium entry caused by TRH may occur through nifedipine/verapamil-insensitive Ca2+ channels.
Lamacz
M
M
Groupe de Recherche en Endocrinologie Moléculaire, UA CNRS 650, Unité Alliée à l'INSERM, Université de Rouen, Mont-Saint-Aignan, France.
Tonon
M C
MC
Louiset
E
E
Desrues
L
L
Cazin
L
L
Guy
J
J
Pelletier
G
G
Vaudry
H
H
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010477:Perfusion; D010902:Pituitary Gland / Q000378:metabolism*; D011863:Radioimmunoassay; D011895:Rana ridibunda; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors
D000001:Calcimycin; D003035:Cobalt; D013973:Thyrotropin-Releasing Hormone; D009074:Melanocyte-Stimulating Hormones; D009543:Nifedipine; D002118:Calcium