Follicle-stimulating hormone evokes an increase in intracellular free calcium ion concentrations in single ovarian (granulosa) cells

Cytosolic free Ca²⁺ ion concentrations were ([Ca²⁺]i) measured in single swine granulosa cells using the Ca²⁺-sensitive fluorescent indicator dye fura-2 and digital imaging videomicroscopy with high spatial and temporal resolution. Ovine FSH (oFSH) elicited specific [Ca²⁺]i increases, which reached their highest value within 5 min of the onset of stimulation and were sustained for 10-15 min. [Ca²⁺]i usually returned to prestimulated levels and cells regained full responsiveness to a second exposure to oFSH within 20 min. The effect of FSH was not blocked by pretreatment with pertussis toxin. Forskolin and 8-bromo-cAMP were able to mimic similar increases in [Ca²⁺]i in the presence or absence of extracellular Ca²⁺. In contrast, the oFSH-induced [Ca²⁺]i rises were abolished in the absence of extracellular Ca²⁺. The Ca²⁺ channel blocker verapamil completely abolished the oFSH-induced [Ca²⁺]i rise, but not the 8-bromo-cAMP- or the forskolin-induced [Ca²⁺]i rise. In summary, we have demonstrated that [Ca²⁺]i is regulated by oFSH in single swine granulosa cells. We propose that the transducing pathway for this FSH effect might not involve cAMP, and that whichever second messenger is responsible for the Ca²⁺ signal generation acts upon plasma membrane Ca²⁺ channels.