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(189) CHARACTERIZATION OF THE INTRACELLULAR CALCIUM STORE AT THE BASE OF THE SPERM TAIL THAT MAY REGULATE HYPERACTIVATED MOTILITY. Ho, Han-Chen1, Suarez, Susan1, 1 Dept of Biomedical Sciences, Ithaca, NY ABSTRACT- Hyperactivated sperm motility is characterized by asymmetrical flagellar beating and is known to be regulated by Ca2+. There is evidence that an inositol 1,4,5-trisphosphate (IP3) receptor-gated Ca2+ store in the base of the flagellum provides Ca2+ to initiate hyperactivation; however, the identity of the store was not known. Ca2+ stores are membrane-bounded organelles. The only two membrane-bounded organelles found in this region of sperm are the redundant nuclear envelope (RNE) and mitochondria. Transmission electron micrographs revealed two different compartments of RNE: one enriched with nuclear pores (NP) and the other containing few pores but extensive membranous structures with enlarged cisternae (EC). Immunolabeling showed that the IP3 receptors are located in the EC-RNE and not in mitochondria. In other cell types, mitochondria adjacent to Ca2+ stores are actively involved in modulating Ca2+ signals by taking up Ca2+ released from stores and also may respond by increasing production of NADH and ATP to support increased energy demand. However, bull sperm did not show an increase in NADH when Ca2+ was released from intracellular stores by 10 KEY WORDS: redundant nuclear envelope, hyperactivation, calcium |
M thapsigargin to induce hyperactivation. Consistantly, no increased ATP production was detected when sperm were hyperactivated, although ATP was hydrolyzed at a greater rate (ATP+ADP+AMP concentrations [nmoles/108 sperm]: control: 97±12; hyperactivated: 97±10, P > 0.05; ATP concentrations: control: 69±6.5; hyperactivated:62±4.5, P < 0.05, n=5). Furthermore, blocking Ca2+ efflux from mitochondria by CGP-37157, a specific inhibitor of mitochondrial Na+/Ca2+ exchanger, did not inhibit the development of hyperactivated motility. We concluded that the intracellular Ca2+ store is EC-RNE and that it may induce hyperactivation without the participation of mitochondria. (NSF grant #MCB0090950)