Calcium elevation in sheep cumulus-oocyte complexes after luteinising hormone stimulation.
We investigated Ca2+ levels in intact cumulus-oocyte complexes (COCs) on exposure to peak levels of luteinising hormone (LH). Specific preparations were used where cumulus corona cells were loaded with a membrane-permeant Ca(2+)-sensitive dye (FLUO-3AM), whereas the oocyte was injected directly with the nonpermeant form of the dye (FLUO-3). After exposure to LH, cumulus and corona radiata cells showed distinct rises in intracellular Ca2+ in 50-200 sec. The pattern of Ca2+ response varied in the different cells both for the duration of the transients and for their persistence. Interestingly, Ca2+ elevations were recorded in all the layers of the cumulus mass, including the innermost layer of corona cells, demonstrating the wide diffusion of LH receptors. Following the Ca2+ raise in somatic cells, an intracellular Ca2+ elevation also was recorded within the oocyte with a delay of 100-300 sec. The elevation started at the cortex of the oocyte and then spread all over the ooplasm. The addition of verapamil or manganese chloride did not prevent LH-induced Ca2+ elevation in the COC, whereas mechanical uncoupling of cumulus cells from the oocyte prevented any Ca2+ response within the oocyte. The results indicate that cumulus corona cells are capable of transducing LH message by rising intracellular Ca2+ and show that this signal is rapidly transferred into the oocyte through gap junctions. This may result from the direct diffusion of Ca2+ or its putative releaser IP3 from cumulus cells to the oocyte.
Mattioli
M
M
Istituto di Fisiologia Veterinaria, Facoltà di Medicina Veterinaria, Università degli Studi di Teramo, Italy.
Gioia
L
L
Barboni
B
B
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D007986:Luteinizing Hormone / Q000378:metabolism* / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep
D007986:Luteinizing Hormone; D002118:Calcium