Thapsigargin increases cytoplasmic free Ca2+ without influencing steroidogenesis in chicken granulosa cells.
The effects of thapsigargin on intracellular Ca2+ concentration ([Ca2+]i) and progesterone production were determined in granulosa cells from the two largest preovulatory follicles of laying hens. [Ca2+]i was measured in cells loaded with the Ca(2+)-responsive fluorescent dye Fura-2. Thapsigargin stimulated a 4.6 +/- 0.2-fold increase in [Ca2+]i from a resting level of 55 +/- 6 nM up to 233 +/- 23 nM (n = 8) in 100% of the cells tested (n = 86). However, two different response patterns were observed. Dependent on the cell populations, a maximally effective concentration of thapsigargin (100 nM) stimulated either a rapid (within 16 +/- 2 s) transient increase in [Ca2+]i or a slowly (99 +/- 20 s) developing and sustained increase in [Ca2+]i. Both [Ca2+]i responses were concentration (0.001-1 microM)-dependent with an EC50 around 40 nM. The transient [Ca2+]i response occurred in the absence of extracellular Ca2+ and was unaffected by pretreating the cells with the Ca2+ channel blockers methoxyverapamil (50 microM) or lanthanum (1 mM). The plateau phase of the sustained [Ca2+]i response returned to resting level in the absence of extracellular Ca2+, but remained elevated in the presence of methoxyverapamil (50 microM) or lanthanum (1 mM). Despite its ability to cause transient or prolonged increases in [Ca2+]i, thapsigargin (0.001-1 microM) did not affect basal or luteinizing hormone-stimulated progesterone production by chicken granulosa cells.
Morley
P
P
Department of Obstetrics and Gynecology and Physiology, University of Ottawa, Ontario, Canada.
Tsang
B K
BK
Whitfield
J F
JF
Schwartz
J L
JL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D005260:Female; D006107:Granulosa Cells / Q000378:metabolism*; D011374:Progesterone / Q000096:biosynthesis*; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
D013729:Terpenes; D011374:Progesterone; D019284:Thapsigargin; D002118:Calcium