Gonadotropin-releasing hormone induced Ca2+ influx in nonsecreting pituitary adenoma cells: role of voltage-dependent Ca2+ channels and protein kinase C.
The action mechanism of gonadotropin-releasing hormone (GnRH) on the cytosolic free calcium concentration ([Ca2+]i) and high-threshold voltage-dependent Ca2+ channel activity was studied in human nonsecreting (NS) pituitary adenoma cells. [Ca2+]i was monitored in individual cells by dual emission microspectrofluorimetry using indo 1 as intracellular fluorescent Ca2+ probe. The whole-cell recording patch-clamp technique was used to study Ca2+ channels. A short application of GnRH (1 to 100 nM) induced an increase in [Ca2+]i due to Ca2+ entry through plasma membrane voltage-sensitive L-type Ca2+ channels. Protein kinase C (PKC) depletion induced by a pretreatment with 1 microM PMA for 24 h abolished spontaneous Ca2+ transients and the action of GnRH on [Ca2+]i and Ca2+ channels. Phloretin (250 microM) and staurosporine (20 nM), two protein kinase C inhibitors, inhibited Ca2+ channel activity, thereby suppressing the effect of GnRH. On the other hand, activation of PKC by a short application of phorbol myristate acetate (10 nM) stimulated Ca2+ influx through Ca2+ channels. These findings demonstrate that, in human NS adenoma cells, GnRH (1 to 100 nM) induces an increase in [Ca2+]i, principally due to Ca2+ entry through L-type voltage-activated Ca2+ channels. PKC regulates this mechanism as well as basal ion channel activity, thus exerting both positive and negative control of [Ca2+]i in stimulated and unstimulated NS adenoma cells.
Prevarskaya
N
N
Laboratory of Neurophysiology, University of Bordeaux II, CNRS URA 1200, France.
Skryma
R
R
Vacher
P
P
Bresson-Bepoldin
L
L
Odessa
M F
MF
Rivel
J
J
San Galli
F
F
Guerin
J
J
Dufy-Barbe
L
L
D000236:Adenoma / Q000378:metabolism* / Q000473:pathology; D000368:Aged; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D004594:Electrophysiology; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008297:Male; D010911:Pituitary Neoplasms / Q000378:metabolism* / Q000473:pathology; D011493:Protein Kinase C / Q000502:physiology*
D015220:Calcium Channels; D007987:Gonadotropin-Releasing Hormone; D011493:Protein Kinase C; D002118:Calcium