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Donner F Babcock

Publications and source records attributed to Donner F Babcock.

5 recordsLinked to original sources
PubMed2004

Sperm-specific protein kinase A catalytic subunit Calpha2 orchestrates cAMP signaling for male fertility.

An unusual cAMP signaling system mediates many of the events that prepare spermatozoa to meet the egg. Its components include the atypical, bicarbonate-stimulated, sperm adenylyl cyclase and a cAMP-dependent protein kinase (PKA) with the unique catalytic subunit termed Calpha(2) or C(s). We generated mice that lack Calpha(2) to determine its importance in the events downstream of cAMP production. Male Calpha(2) null mice produce normal numbers of sperm that swim spontaneously in vitro. Thus, Calpha(2) has no required role in formation of a functional flagellum or the initiation of motility. In contrast, we find that Calpha(2) is required for bicarbonate to speed the flagellar beat and facilitate Ca(2+) entry channels. In addition, Calpha(2) is needed for the protein tyrosine phosphorylation that occurs late in the sequence of sperm maturation and for a negative feedback control of cAMP production, revealed here. Consistent with these specific defects in several important sperm functions, Calpha(2) null males are infertile despite normal mating behavior. These results define several crucial roles of PKA in sperm cell biology, bringing together both known and unique PKA-mediated events that are necessary for male fertility.

Adenylyl Cyclases↗
PubMed2003

CatSper1 required for evoked Ca2+ entry and control of flagellar function in sperm.

CatSper family proteins are putative ion channels expressed exclusively in membranes of the sperm flagellum and required for male fertility. Here, we show that mouse CatSper1 is essential for depolarization-evoked Ca2+ entry and for hyperactivated movement, a key flagellar function. CatSper1 is not needed for other developmental landmarks, including regional distributions of CaV1.2, CaV2.2, and CaV2.3 ion channel proteins, the cAMP-mediated activation of motility by HCO3-, and the protein phosphorylation cascade of sperm capacitation. We propose that CatSper1 functions as a voltage-gated Ca2+ channel that controls Ca2+ entry to mediate the hyperactivated motility needed late in the preparation of sperm for fertilization.

Animals↗
PubMed2003

Calcium clearance mechanisms of mouse sperm.

The spermatozoon is specialized for a single vital role in fertilization. Past studies show that Ca2+ signals produced by the opening of plasma membrane entry channels initiate several events required for the sperm to reach and enter the egg but reveal little about how resting [Ca2+]i is maintained or restored after elevation. We examined these homeostatic mechanisms by monitoring the kinetics of recovery from depolarizing stimuli under conditions intended to inhibit candidate mechanisms for sequestration or extrusion of Ca2+ from the cytosol. We found that the Ca2+-ATPase pump of the plasma membrane performs the major task of Ca2+ clearance. It is essential in the final stages of recovery to achieve a low resting [Ca2+]i. With immunomethods we found a approximately 130-kD plasma membrane Ca2+-ATPase protein on Western blots of whole sperm extracts and showed immunolocalization to the proximal principal piece of the flagellum. The plasma membrane Na+-Ca2+ exchanger also exports Ca2+ when [Ca2+]i is elevated. Simultaneous inhibition of both mechanisms of extrusion revealed an additional contribution to clearance from a CCCP-sensitive component, presumably sequestration by the mitochondria. Involvement of SERCA pumps was not clearly detected. Many aspects of the kinetics of Ca2+ clearance observed in the presence and absence of inhibitors were reproduced in a mathematical model based on known and assumed kinetic parameters. The model predicts that when cytosolic [Ca2+] is at 1 microM, the rates of removal by the Ca2+-ATPase, Na+-Ca2+-exchanger, mitochondrial uniporter, and SERCA pump are approximately 1.0, 0.35, 0.33, and 0 micromole l(-1) s(-1), rates substantially slower than those reported for other cells studied by similar methods. According to the model, the Na+-Ca2+ exchanger is poised so that it may run in reverse at resting [Ca2+]i levels. We conclude that the essential functions of sperm do not require the ability to recover rapidly from globally elevated cytosolic [Ca2+].

Animals↗
PubMed2003

Bicarbonate actions on flagellar and Ca2+ -channel responses: initial events in sperm activation.

At mating, mammalian sperm are diluted in the male and female reproductive fluids, which brings contact with HCO(3)(-) and initiates several cellular responses. We have identified and studied two of the most rapid of these responses. Stop-motion imaging and flagellar waveform analysis show that for mouse epididymal sperm in vitro, the resting flagellar beat frequency is 2-3 Hz at 22-25 degrees C. Local perfusion with HCO(3)(-) produces a robust, reversible acceleration to 7 Hz or more. At 15 mM the action of HCO(3)(-) begins within 5 seconds and is near-maximal by 30 seconds. The half-times of response are 8.8+/-0.2 seconds at 15 mM HCO(3)(-) and 17.5+/-0.4 seconds at 1 mM HCO(3)(-). Removal of external HCO(3)(-) allows a slow return to basal beat frequency over approximately 10 minutes. Increases in beat symmetry accompany the accelerating action of HCO(3)(-). As in our past work, HCO(3)(-) also facilitates opening of voltagegated Ca(2+) channels, increasing the depolarization-evoked rate of rise of intracellular Ca(2+) concentration by more than fivefold. This action also is detectable at 1 mM HCO(3)(-) and occurs with an apparent halftime of approximately 60 seconds at 15 mM HCO(3)(-). The dual actions of HCO(3)(-) respond similarly to pharmacological intervention. Thus, the phosphodiesterase inhibitor IBMX promotes the actions of HCO(3)(-) on flagellar and channel function, and the protein kinase A inhibitor H89 blocks these actions. In addition, a 30 minute incubation with 60 micro M cAMP acetoxylmethyl ester increases flagellar beat frequency to nearly 7 Hz and increases the evoked rates of rise of intracellular Ca(2+) concentration from 17+/-4 to 41+/-6 nM second(-1). However, treatment with several other analogs of cAMP produces only scant evidence of the expected mimicry or blockade of the actions of HCO(3)(-), perhaps as a consequence of limited permeation. Our findings indicate a requirement for cAMP-mediated protein phosphorylation in the enhancement of flagellar and channel functions that HCO(3)(-) produces during sperm activation.

Animals↗