INTRACELLULAR CALCIUM VARIATION IN HEPARIN-CAPACITATED BOVINE SPERM

This report investigates the mechanisms by which heparin induces capac itation of sperm. Capacitation was determined with chlortetracycline a nd intracellular calcium concentration, [Ca2+](i), with FURA 2-AM. Aft er 15 minutes incubation with heparin, [Ca2+](i) was increased 60% ove r basal, reaching a plateau thereafter. Sixty percent of calcium entry was inhibited by methoxy-verapamil, suggesting that activation of vol tage dependent calcium channels (VDCC) may be involved in the process. A significant correlation (R-2 = 0.88, p<0.006) was found between the percentage of capacitated spermarozoa and the [Ca2+](i) increase, The effects of heparin on both processes were blocked by the protein kina se C (PKC) inhibitors staurosporine (100%) and GF-109203X (90%). It is concluded that heparin may induce sperm capacitation and calcium infl ux mainly through VDCC (approx. 60%), and also through other membrane systems (40%). Both systems of calcium entry as well as the capacitati on process appear to involve on PKC activity.