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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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Representative examples of the effect of IBMX treatment on speract-induced [Ca2+]i increases in individual sperm. (A) Effect of IBMX treatment on Ca2+ increase in sperm heads. Images acquired at 10 frames per second with 100-ms individual frame exposure time. (B) Effect of IBMX treatment on [Ca2+]i increase in sperm flagella. Images acquired at 40 frames per second with 25-ms individual frame exposure time. In both A and B, blue traces from sperm treated with 100 μM IBMX before addition of 500 pM speract (indicated by arrow); red trace from non-IBMX–treated sperm. Changes in [Ca2+]i were determined for heads and flagella by pseudo-ratioing their fluorescence (F) against their initial fluorescence (F0).
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fig9: Representative examples of the effect of IBMX treatment on speract-induced [Ca2+]i increases in individual sperm. (A) Effect of IBMX treatment on Ca2+ increase in sperm heads. Images acquired at 10 frames per second with 100-ms individual frame exposure time. (B) Effect of IBMX treatment on [Ca2+]i increase in sperm flagella. Images acquired at 40 frames per second with 25-ms individual frame exposure time. In both A and B, blue traces from sperm treated with 100 μM IBMX before addition of 500 pM speract (indicated by arrow); red trace from non-IBMX–treated sperm. Changes in [Ca2+]i were determined for heads and flagella by pseudo-ratioing their fluorescence (F) against their initial fluorescence (F0).

Mentions: Speract elevates the levels of cGMP and cAMP. These second messengers then modulate sperm ion permeability (reviewed in Darszon et al., 2001). To explore how the levels of these cyclic nucleotides affect the speract-induced [Ca2+]i fluctuations, we used 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cyclic nucleotide phosphodiesterases (Cook and Babcock, 1993a,b). As illustrated in Fig. 9 A, 100 μM IBMX abolishes the speract-induced [Ca2+]i fluctuations, but not the sustained [Ca2+]i increase in the head. However, the kinetic characteristics of the tonic [Ca2+]i increase are altered significantly: t1/2 of tonic elevation in [Ca2+]i is 6.5 ± 0.25 s in IBMX-treated sperm versus 0.98 ± 0.25 s in non-IBMX–treated sperm (n = 17, P < 0.001; unpaired two-tailed t test). In the flagella (Fig. 9 B), the speract-induced phasic fluctuations are abolished, and the small tonic increase in calcium, although sustained, does not gradually increase over time as in the head (n = 8).


Speract induces calcium oscillations in the sperm tail.

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

Representative examples of the effect of IBMX treatment on speract-induced [Ca2+]i increases in individual sperm. (A) Effect of IBMX treatment on Ca2+ increase in sperm heads. Images acquired at 10 frames per second with 100-ms individual frame exposure time. (B) Effect of IBMX treatment on [Ca2+]i increase in sperm flagella. Images acquired at 40 frames per second with 25-ms individual frame exposure time. In both A and B, blue traces from sperm treated with 100 μM IBMX before addition of 500 pM speract (indicated by arrow); red trace from non-IBMX–treated sperm. Changes in [Ca2+]i were determined for heads and flagella by pseudo-ratioing their fluorescence (F) against their initial fluorescence (F0).
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Related In: Results  -  Collection

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fig9: Representative examples of the effect of IBMX treatment on speract-induced [Ca2+]i increases in individual sperm. (A) Effect of IBMX treatment on Ca2+ increase in sperm heads. Images acquired at 10 frames per second with 100-ms individual frame exposure time. (B) Effect of IBMX treatment on [Ca2+]i increase in sperm flagella. Images acquired at 40 frames per second with 25-ms individual frame exposure time. In both A and B, blue traces from sperm treated with 100 μM IBMX before addition of 500 pM speract (indicated by arrow); red trace from non-IBMX–treated sperm. Changes in [Ca2+]i were determined for heads and flagella by pseudo-ratioing their fluorescence (F) against their initial fluorescence (F0).
Mentions: Speract elevates the levels of cGMP and cAMP. These second messengers then modulate sperm ion permeability (reviewed in Darszon et al., 2001). To explore how the levels of these cyclic nucleotides affect the speract-induced [Ca2+]i fluctuations, we used 3-isobutyl-1-methylxanthine (IBMX), an inhibitor of cyclic nucleotide phosphodiesterases (Cook and Babcock, 1993a,b). As illustrated in Fig. 9 A, 100 μM IBMX abolishes the speract-induced [Ca2+]i fluctuations, but not the sustained [Ca2+]i increase in the head. However, the kinetic characteristics of the tonic [Ca2+]i increase are altered significantly: t1/2 of tonic elevation in [Ca2+]i is 6.5 ± 0.25 s in IBMX-treated sperm versus 0.98 ± 0.25 s in non-IBMX–treated sperm (n = 17, P < 0.001; unpaired two-tailed t test). In the flagella (Fig. 9 B), the speract-induced phasic fluctuations are abolished, and the small tonic increase in calcium, although sustained, does not gradually increase over time as in the head (n = 8).

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