Intracellular calcium and the signaling mechanism of luteinizing hormone-releasing hormone in rat granulosa cells.
OBJECTIVE
The purpose of these studies was to determine the source(s) of the increase in intracellular free calcium in response to luteinizing hormone-releasing hormone in ovarian granulosa cells.


METHODS
Rat granulosa cells were cultured and loaded with fura-2-acetoxy-methyl ester, a fluorescent calcium indicator dye, and intracellular free calcium measured by microspectrofluorometry. The source of the luteinizing hormone-releasing hormone induced increase in intracellular Ca++ was investigated with various calcium channel blockers (verapamil, diltiazem, and nifedipine), high K+ buffer, and perifusion with media lacking Ca++.


RESULTS
All three voltage-sensitive calcium channel blockers (10(-5) mol/L) tested were ineffective in blocking the luteinizing hormone-releasing hormone induced intracellular Ca++ increase. Treatment with high K+ buffer also had no effect. Perifusion with media lacking calcium resulted in a gradual loss of the luteinizing hormone-releasing hormone response, an effect that was accelerated by repeated stimulation with hormone. Transient replacement of extracellular Ca++ failed to restore the response but continued perifusion with Ca(++)-replete media allowed a luteinizing hormone-releasing hormone response 10 minutes later.


CONCLUSIONS
The luteinizing hormone-releasing hormone induced intracellular Ca++ increase does not appear to result from the opening of voltage-sensitive or K(+)-dependent Ca++ channels. To the contrary, this response likely results from the release of Ca++, primarily from intracellular stores.
Wang
J
J
Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, Canada.
Steele
G L
GL
Baimbridge
K G
KG
Rodway
M R
MR
Leung
P C
PC
D000818:Animals; D002021:Buffers; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology / Q000502:physiology*; D006107:Granulosa Cells / Q000378:metabolism / Q000502:physiology*; D007425:Intracellular Membranes / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction; D012965:Sodium Chloride / Q000494:pharmacology
D002021:Buffers; D002121:Calcium Channel Blockers; D007987:Gonadotropin-Releasing Hormone; D012965:Sodium Chloride; D011188:Potassium; D002118:Calcium