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Speract induces calcium oscillations in the sperm tail.

Wood CD, Darszon A, Whitaker M - J. Cell Biol. (2003)

Bottom Line: These data point to a model in which a messenger generated periodically in the tail diffuses to the head.Sperm are highly polarized cells.Our results indicate that a clear understanding of the link between [Ca2+]i and sperm motility will only be gained by analysis of [Ca2+]i signals at the level of the single sperm.

View Article: PubMed Central - PubMed

Affiliation: School of Cell and Molecular Biosciences, University of Newcastle upon Tyne, NE2 4HH, UK.

ABSTRACT
Sea urchin sperm motility is modulated by sperm-activating peptides. One such peptide, speract, induces changes in intracellular free calcium concentration ([Ca2+]i). High resolution imaging of single sperm reveals that speract-induced changes in [Ca2+]i have a complex spatiotemporal structure. [Ca2+]i increases arise in the tail as periodic oscillations; [Ca2+]i increases in the sperm head lag those in the tail and appear to result from the summation of the tail signal transduction events. The period depends on speract concentration. Infrequent spontaneous [Ca2+]i transients were also seen in the tail of unstimulated sperm, again with the head lagging the tail. Speract-induced fluctuations were sensitive to membrane potential and calcium channel blockers, and were potentiated by niflumic acid, an anion channel blocker. 3-isobutyl-1-methylxanthine, which potentiates the cGMP/cAMP-signaling pathways, abolished the [Ca2+]i fluctuations in the tail, leading to a very delayed and sustained [Ca2+]i increase in the head. These data point to a model in which a messenger generated periodically in the tail diffuses to the head. Sperm are highly polarized cells. Our results indicate that a clear understanding of the link between [Ca2+]i and sperm motility will only be gained by analysis of [Ca2+]i signals at the level of the single sperm.

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The degree and characteristics of speract-induced increases in [Ca2+]i are altered by both increasing and decreasing [K+]e. (A) For each sperm head, the ratio increase in [Ca2+]i was determined from the maximum fluorescence intensity after addition of speract to a final concentration of 500 pM (Fmax) and the initial fluorescence intensity value (F0). Fmax/F0 is presented as the average of all sperm heads analyzed (total number of sperm heads at each [K+]e shown in brackets). Error bars represent ± SEM. (B) Typical responses in individual sperm heads at different [K+]e. F/F0 shown over time after addition of speract to a final concentration of 500 pM (indicated by arrow). Images acquired at 10 frames per second with 100-ms individual frame exposure time. One-tailed t test (comparison to 10 mM data) ***, P < 0.001; *, P < 0.05.
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fig6: The degree and characteristics of speract-induced increases in [Ca2+]i are altered by both increasing and decreasing [K+]e. (A) For each sperm head, the ratio increase in [Ca2+]i was determined from the maximum fluorescence intensity after addition of speract to a final concentration of 500 pM (Fmax) and the initial fluorescence intensity value (F0). Fmax/F0 is presented as the average of all sperm heads analyzed (total number of sperm heads at each [K+]e shown in brackets). Error bars represent ± SEM. (B) Typical responses in individual sperm heads at different [K+]e. F/F0 shown over time after addition of speract to a final concentration of 500 pM (indicated by arrow). Images acquired at 10 frames per second with 100-ms individual frame exposure time. One-tailed t test (comparison to 10 mM data) ***, P < 0.001; *, P < 0.05.

Mentions: Cells that undergo membrane potential (Em) and [Ca2+]i oscillations are known to possess an appropriate battery of voltage-dependent ion channels (Gauss et al., 1998). There is evidence suggesting that sea urchin sperm posses a set of such channels: blockers of voltage-dependent cation channels (VDCCs) like Ni2+ and dihydropyridines, and of K+ channels, like TEA+, inhibit the acrosome reaction (AR), indicating that these channels are present in sperm. (Darszon et al., 2001). We investigated whether maneuvers that alter sperm Em influence the speract-induced fluctuations in [Ca2+]i. The external concentration of K+ ([K+]e) was varied to modify the resting and speract-induced Em of sea urchin sperm (Babcock et al., 1992; González-Martinez et al., 1992). Fig. 6 shows how the magnitude of the tonic change in [Ca2+]i (A) and the [Ca2+]i fluctuations (B) induced by 500 pM speract are affected by [K+]e. When K+ is removed from seawater, the speract-induced fluctuations disappear, though the tonic response is enhanced in magnitude (n = 35). High [K+]e is known to eliminate all speract responses, but the increase in cGMP (Schackmann and Chock, 1986; Harumi et al., 1992), elevating [K+]e to 20 mM as anticipated, inhibits both tonic and phasic speract responses (n = 68). These findings emphasize the importance of the sperm Em in the generation of the [Ca2+]i fluctuations as part of the speract response.


Speract induces calcium oscillations in the sperm tail.

Wood CD, Darszon A, Whitaker M - J. Cell Biol. (2003)

The degree and characteristics of speract-induced increases in [Ca2+]i are altered by both increasing and decreasing [K+]e. (A) For each sperm head, the ratio increase in [Ca2+]i was determined from the maximum fluorescence intensity after addition of speract to a final concentration of 500 pM (Fmax) and the initial fluorescence intensity value (F0). Fmax/F0 is presented as the average of all sperm heads analyzed (total number of sperm heads at each [K+]e shown in brackets). Error bars represent ± SEM. (B) Typical responses in individual sperm heads at different [K+]e. F/F0 shown over time after addition of speract to a final concentration of 500 pM (indicated by arrow). Images acquired at 10 frames per second with 100-ms individual frame exposure time. One-tailed t test (comparison to 10 mM data) ***, P < 0.001; *, P < 0.05.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172867&req=5

fig6: The degree and characteristics of speract-induced increases in [Ca2+]i are altered by both increasing and decreasing [K+]e. (A) For each sperm head, the ratio increase in [Ca2+]i was determined from the maximum fluorescence intensity after addition of speract to a final concentration of 500 pM (Fmax) and the initial fluorescence intensity value (F0). Fmax/F0 is presented as the average of all sperm heads analyzed (total number of sperm heads at each [K+]e shown in brackets). Error bars represent ± SEM. (B) Typical responses in individual sperm heads at different [K+]e. F/F0 shown over time after addition of speract to a final concentration of 500 pM (indicated by arrow). Images acquired at 10 frames per second with 100-ms individual frame exposure time. One-tailed t test (comparison to 10 mM data) ***, P < 0.001; *, P < 0.05.
Mentions: Cells that undergo membrane potential (Em) and [Ca2+]i oscillations are known to possess an appropriate battery of voltage-dependent ion channels (Gauss et al., 1998). There is evidence suggesting that sea urchin sperm posses a set of such channels: blockers of voltage-dependent cation channels (VDCCs) like Ni2+ and dihydropyridines, and of K+ channels, like TEA+, inhibit the acrosome reaction (AR), indicating that these channels are present in sperm. (Darszon et al., 2001). We investigated whether maneuvers that alter sperm Em influence the speract-induced fluctuations in [Ca2+]i. The external concentration of K+ ([K+]e) was varied to modify the resting and speract-induced Em of sea urchin sperm (Babcock et al., 1992; González-Martinez et al., 1992). Fig. 6 shows how the magnitude of the tonic change in [Ca2+]i (A) and the [Ca2+]i fluctuations (B) induced by 500 pM speract are affected by [K+]e. When K+ is removed from seawater, the speract-induced fluctuations disappear, though the tonic response is enhanced in magnitude (n = 35). High [K+]e is known to eliminate all speract responses, but the increase in cGMP (Schackmann and Chock, 1986; Harumi et al., 1992), elevating [K+]e to 20 mM as anticipated, inhibits both tonic and phasic speract responses (n = 68). These findings emphasize the importance of the sperm Em in the generation of the [Ca2+]i fluctuations as part of the speract response.

Bottom Line: These data point to a model in which a messenger generated periodically in the tail diffuses to the head.Sperm are highly polarized cells.Our results indicate that a clear understanding of the link between [Ca2+]i and sperm motility will only be gained by analysis of [Ca2+]i signals at the level of the single sperm.

View Article: PubMed Central - PubMed

Affiliation: School of Cell and Molecular Biosciences, University of Newcastle upon Tyne, NE2 4HH, UK.

ABSTRACT
Sea urchin sperm motility is modulated by sperm-activating peptides. One such peptide, speract, induces changes in intracellular free calcium concentration ([Ca2+]i). High resolution imaging of single sperm reveals that speract-induced changes in [Ca2+]i have a complex spatiotemporal structure. [Ca2+]i increases arise in the tail as periodic oscillations; [Ca2+]i increases in the sperm head lag those in the tail and appear to result from the summation of the tail signal transduction events. The period depends on speract concentration. Infrequent spontaneous [Ca2+]i transients were also seen in the tail of unstimulated sperm, again with the head lagging the tail. Speract-induced fluctuations were sensitive to membrane potential and calcium channel blockers, and were potentiated by niflumic acid, an anion channel blocker. 3-isobutyl-1-methylxanthine, which potentiates the cGMP/cAMP-signaling pathways, abolished the [Ca2+]i fluctuations in the tail, leading to a very delayed and sustained [Ca2+]i increase in the head. These data point to a model in which a messenger generated periodically in the tail diffuses to the head. Sperm are highly polarized cells. Our results indicate that a clear understanding of the link between [Ca2+]i and sperm motility will only be gained by analysis of [Ca2+]i signals at the level of the single sperm.

Show MeSH
Related in: MedlinePlus