Sperm factor initiates capacitance and conductance changes in mouse eggs that are more similar to fertilization than IP(3)- or Ca(2+)-induced changes.
We used patch clamp electrophysiology and concurrent imaging with the Ca(2+)-sensitive dye, fura-2, to study the temporal relationship between membrane capacitance and conductance and intracellular free Ca(2+) concentration ([Ca(2+)](i)) during mouse egg fertilization. We found an approximately 2 pF step increase in egg membrane capacitance and a minor increase in conductance with no change in [Ca(2+)](i) at sperm fusion. This was followed approximately 1 min later by a rise in [Ca(2+)](i) that led to larger changes in capacitance and conductance. The most common pattern for these later capacitance changes was an initial capacitance decrease, followed by a larger increase and eventual return to the approximate starting value. There was some variation in this pattern, and sub-microM peak [Ca(2+)](i) favored capacitance decrease, while higher [Ca(2+)](i) favored capacitance increase. The magnitude of accompanying conductance increases was variable and did not correlate well with peak [Ca(2+)](i). The intracellular introduction of porcine sperm factor reproduced the postfusion capacitance and conductance changes with a similar [Ca(2+)](i) dependence. Raising [Ca(2+)](i) by the intracellular introduction of IP(3) initiated fertilization-like capacitance changes, but the conductance changes were slower to activate. Capacitance decrease could be induced when [Ca(2+)](i) was increased modestly by activation of an endogenous Ca(2+) current, with little effect on resting conductance. These results suggest that net turnover of the mouse egg surface membrane is sensitive to [Ca(2+)](i) and that sperm and the active component of sperm factor may be doing more than initiating the IP(3)-mediated release of intracellular Ca(2+).
Section of Molecular and Cellular Biology, University of California, Davis, California, 95616, USA.
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Lee
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Fissore
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Nuccitelli
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D004553:Electric Conductivity; D005260:Female; D005306:Fertilization; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D007476:Ionophores / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D011493:Protein Kinase C / Q000502:physiology; D013084:Sperm-Ovum Interactions; D013552:Swine
D002712:Chlorides; D007476:Ionophores; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D002118:Calcium