Involvement of voltage-dependent calcium channels (VDCC) in the action of GnRH on GtH release in common carp (Cyprinus carpio L): comparison with K+ action.
The involvement of different types of voltage-dependent calcium channels (VDCC) in the stimulatory action of GnRH (in comparison with K+) on maturational gonadotropin (GtH) release was investigated using superfused carp pituitary cells. The action of these 2 stimulants was not modified either by D600 or nifedipine (drugs blocking L-type of VDCC). Cadmium (Cd2+), which blocks all types of VDCC indifferently, provoked a dose-dependent stimulation of GtH secretion. Cd2+ action was not altered by addition of sGnRH in any of the doses. Similar results were obtained using K+ as a secretagogue, but only the highest dose of Cd2+ (200 mumol/l) was able to completely block K+ action. Low doses (0.1 and 1 mumol/l) of the L-type VDCC activator BAY-K8644 did not change basal GtH secretion and had no effect on sGnRH-stimulated GtH secretion. Surprisingly, doses (10 mumol/l and higher) of BAY-K8644 evoked dose-dependent inhibition of GtH secretion. On the other hand, a higher concentration (20 mumol/l) of nifedipine provoked a stimulation of GtH release. Our results indicate that the stimulatory action of GnRH and K+ involves activation of a certain type of cadmium-sensitive VDCC (probably T- or N-type VDCC) whereas dihydropyridine and diphenylalkylamine sensitive VDCC (L-type VDCC) does not participate in this phenomenon. The inhibitory action of BAY-K8644 and, on the other hand, the stimulatory action of nifedipine indicate that L-type VDCC probably play a role in other physiological pathways regulating GtH release in carp.
Mikolajczyk
T
T
INRA, Laboratoire de Physiologie des Poissons, Rennes, France.
Weil
C
C
Epler
P
P
Breton
B
B
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002347:Carps / Q000502:physiology*; D005711:Gallopamil / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology
D015220:Calcium Channels; D006065:Gonadotropins, Pituitary; D002104:Cadmium; D007987:Gonadotropin-Releasing Hormone; D005711:Gallopamil; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009543:Nifedipine; D011188:Potassium