Intracellular calcium accumulation and responsiveness to progesterone in capacitating human spermatozoa.
Progesterone induced a rapid, long-lasting, dose-dependent increase of intracellular free calcium concentration ([Ca2+]i) in human sperm capacitated overnight. This effect was not counteracted by the cytosolic progesterone receptor antagonist RU486 (1 mumol/L) nor by the GABA-A receptor antagonists bicuculline (10 mumol/L) and picrotoxin (50 mumol/L). Also, the rank order of potency of several progestative steroids on [Ca2+]i differed from that previously reported for uterine intracellular progesterone receptor or for P-GABA interaction in the central nervous system, indicating a different pathway for progesterone stimulation of human sperm. Modifications of basal and progesterone-stimulated [Ca2+]i during sperm capacitation were also studied. A progressive, parallel increase of basal and progesterone-stimulated [Ca2+]i in capacitating spermatozoa was found. In particular, progesterone-stimulated [Ca2+]i increased from a basal concentration of 147% +/- 17% at 10 minutes to 327% +/- 65% after 120 minutes of incubation in capacitating medium. This increase was well correlated with basal [Ca2+]i (r = 0.93). In contrast, basal and progesterone-stimulated [Ca2+]i concentrations were constantly low in spermatozoa incubated in noncapacitating medium. In capacitated spermatozoa, initial responsiveness to progesterone and basal [Ca2+]i was higher than in capacitating and noncapacitated samples, and remained constant throughout the duration of the experiment. The progressive, parallel increase of [Ca2+]i and response to progesterone observed during in vitro capacitation of human spermatozoa might be physiologically relevant in vivo during capacitation of sperm in the female genital tract.
Baldi
E
E
Department of Clinical Pathophysiology, University of Florence, Italy.
Casano
R
R
Falsetti
C
C
Krausz
C
C
Maggi
M
M
Forti
G
G
D001640:Bicuculline / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016257:Fura-2 / Q000031:analogs & derivatives; D006801:Humans; D008297:Male; D015735:Mifepristone / Q000494:pharmacology; D010758:Phosphorus / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D013075:Sperm Capacitation / Q000187:drug effects / Q000502:physiology*; D013094:Spermatozoa / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*
D001640:Bicuculline; D000001:Calcimycin; D002118:Calcium; D016257:Fura-2; D015735:Mifepristone; D010758:Phosphorus; D010852:Picrotoxin; D011374:Progesterone; C049925:fura-2-am