Effect of FSH and progesterone on human spermatozoa cytosolic calcium

Ejaculated spermatozoa must undergo a number of modifications before fertilizing the oocyte: among these the capacitation and the acrosome reaction. Calcium signals play an essential role in these functional and structural modifications. Mature spermatozoa have few organelles and a very small cytoplasmic volume but maintain the homeostasis of [Ca2+]c with great accuracy. We study Ca2+ mobilization in human spermatozoa exposed to FSH and progesterone by measuring the [Ca2+]c with the FURA-2AM method and report for the first time that the exposure to FSH (up to 98 ng/ml) produced an increase of [Ca2+]c to an extent comparable to that observed with 1 μM progesterone. FSH and progesterone increase the spermatozoa [Ca2+]c by acting primarily on calcium entry from the external medium. The effects of the two hormones on [Ca2+]c were similar but not identical; the pre-treatment of progesterone blocks the effects of FSH, but not vice-versa. The increase of [Ca2+]c due to FSH was more sensitive to nifedipine (VOCCs inhibitor) than that of progesterone. The effects of these hormones on calcium homeostasis may be relevant for sperm activation.