We have investigated at the single-cell level how the human LH receptor mediates a dose-responsive increase in intracellular free calcium-ion concentrations ([Ca 2+](i)). In human embryonic kidney cells (293 cells) stably transfected with the full-length human LH receptor cDNA. Intact dimeric LH, but not LH β- or α-subunits, evoked specific [Ca 2+](i) signals. High-resolution fluorescence (fura-2) video-microscopy demonstrated cell-to-cell variability in [Ca 2+](i) signaling responses in individual cells, viz., an all-or-none spike (9%), spike-and-plateau (25%), or plateau (52%) types of temporal signal. Oscillatory [Ca 2+](i) responses were observed in 12-14% of LH-stimulated cells unrelated to LH concentration. The LH dose-response originated by higher concentrations of LH recruiting more individually responding cells (rather than altering [Ca 2+](i) signal amplitude), and eliciting a [Ca 2+](i) rise more rapidly, i.e., at reduced latency. Cobalt did not abolish the LH-stimulated [Ca 2+](i) spike-and- plateau response, but decreased the percentage of cells with a plateau pattern. Quench experiments demonstrated influx of Mn 2+ following the [Ca 2+](i) spike, thus directly documenting divalent cation inflow during the plateau phase. Adenylyl-cyclase activation with forskolin or treatment with a cAMP analog failed to elicit the biphasic [Ca 2+](i) response, and pertussis toxin (PTX) did not alter LH-stimulated [Ca 2+](i) signaling. However, overnight preincubation with LH reduced the percentage of [Ca 2+](i)-responding cells following re-exposure to LH to 5.7% (vs 72% in control), suggesting LH-induced desensitization of the LH-receptor directed [Ca 2+](i) signal. In summary, the present studies of human LH receptor signal transduction at the single-cell level show that increasing concentrations of LH achieve a dose-dependent intracellular Ca 2+ signaling response by recruiting an increasing number of [Ca 2+](i)-responding cells, while concomitantly decreasing the temporal latency of the biphasic [Ca 2+](i) signal without altering the amplitude of its spike phase. Prolonged exposure to LH appears to desensitize the LH receptor-driven [Ca 2+](i) signal.
|Original language||English (US)|
|Number of pages||8|
|State||Published - 1997|
ASJC Scopus subject areas