Spontaneous and gonadotropin-releasing hormone-stimulated cytosolic calcium rises in individual goldfish gonadotrophs.
The cytosolic free calcium concentration, [Ca2+]i, was monitored in single isolated goldfish gonadotrophs with the fluorescent probe Indo-1. It was found that goldfish gonadotrophs exhibit both spontaneous and secretagogue-induced [Ca2+]i rises. Spontaneous [Ca2+]i transients showed striking kinetic features and a sensitivity to external Ca2+ suggesting that they were the consequence of transient Ca2+ entries. Two kinetically distinct patterns of [Ca2+]i rises were generated in response to the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II). In a part of the gonadotrophs, GnRHs triggered a plateau [Ca2+]i rise whereas in other responsive cells they induced a series of [Ca2+]i bursts, each consisting of grouped [Ca2+]i transients. Both plateau and burst [Ca2+]i response patterns were due to Ca2+ entry through plasma membrane Ca2+ channels, inasmuch as they were suppressed with external Ca2+ removal. No contribution of Ca2+ release from thapsigargin-sensitive stores was observed in either response pattern. While in mammalian gonadotrophs GnRH rises [Ca2+] by mostly acting on internal Ca2+ sequestering stores, our results show that GnRH-stimulated goldfish gonadotrophs rapidly increase Ca2+ entry to enhance their [Ca2+]i levels.
Mollard
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P
CNRS URA 1200, Université de Bordeaux II, France. mollard@u401.montp.inserm.fr
Kah
O
O
D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006054:Goldfish; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology*; D017275:Isradipine / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000378:metabolism*; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D026941:Sodium Channel Blockers; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D019284:Thapsigargin; C047717:LHRH, His(5)-Trp(7)-Tyr(8)-; D000252:Calcium-Transporting ATPases; D002118:Calcium; D017275:Isradipine