Journal
DEVELOPMENTAL BIOLOGY
Volume 312, Issue 1, Pages 183-192Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ydbio.2007.09.017
Keywords
NP-EGTA; cyclic AMP; capacitation; CA-II; CAH2; sAC; uncaging
Categories
Funding
- NICHD NIH HHS [U54 HD012629-27, U54 HD12629, U54 HD012629] Funding Source: Medline
- NIGMS NIH HHS [T32 GM07270] Funding Source: Medline
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The HCO3- anion activates sperm motility, an important early step in capacitation, by increasing flagellar beat frequency through a pathway that requires the atypical adenylyl cyclase SACY and the sperm-specific C alpha(2) catalytic subunit of PKA. Here we show that the accelerating action of HCO3- also requires the continued presence of external Ca2+ (EC50 similar to 0.5 mM), and find that Ca2+ can be replaced by Sr2+ but not by Mn2+. Ca2+ is required for HCO3- to elevate cAMP, but not for cAMP-AM to increase beat frequency, indicating that external Ca2+ acts before rather than after stimulation of SACY by HCOT. With external Ca2+ present, HCO3- does not alter cytosolic or near-membrane [Ca2+]. Retrieval of external Ca2+ initiates a slow decline in intracellular [Ca2+] and rapid block of the HCO(3)(-)evoked acceleration that is not relieved upon increasing internal [Ca2+] by rapid photolysis of caged Ca2+. We also find that the rapid (t(1/2) similar to 10 s) accelerating action of HCO3- is slowed more than three-fold by the carbonic anhydrase inhibitor acetazolamide. It is unaltered by the broad spectrum anion transport inhibitor SITS, and is not accompanied by detectable changes in intracellular pH. We propose that external Ca2+ binds an unidentified extracellular protein that is required for HCO3- to engage cAMP-mediated activation of motility. Published by Elsevier Inc.
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