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1 October 2002 Na /Ca2 Exchanger in Porcine Oocytes
Zoltán Macháty, Jagdeece J. Ramsoondar, Aaron J. Bonk, Randall S. Prather, Kenneth R. Bondioli
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The presence of the Na /Ca2 exchange mechanism was investigated in porcine oocytes. Immature and in vitro-matured oocytes were loaded with the Ca2 -sensitive fluorescent dye fura 2 and changes in the intracellular free Ca2 concentration ([Ca2 ]i) were monitored after altering the Na concentration gradient across the plasma membrane. Decreasing the extracellular Na concentration induced an increase in [Ca2 ]i possibly by a Ca2 influx via the Na /Ca2 exchanger. A similar Ca2 influx could also be triggered after increasing the intracellular Na concentration by incubation in the presence of ouabain (0.4 mM), a Na /K -ATPase inhibitor. The increase in the [Ca2 ]i was due to Ca2 influx since it was abolished in the absence of extracellular Ca2 , and the increase was mediated by the Na /Ca2 exchanger since it was blocked by the application of amiloride or bepridil, inhibitors of Na /Ca2 exchange. Verapamil (50 μM) and pimozide (50 μM), inhibitors of L- and T-type voltage-gated Ca2 channels, respectively, could not block the Ca2 influx. The Ca2 entry via the Na /Ca2 exchanger could not induce the release of cortical granules and did not stimulate the resumption of meiosis. This was unexpected because Ca2 is thought to be a universal trigger for activation. Using antibodies raised against the exchanger, it was demonstrated that the Na /Ca2 exchanger was localized predominantly in the plasma membrane. Reverse transcription-polymerase chain reaction revealed that porcine oocytes contain a transcript that shows 98.1% homology to the NACA3 isoform of the porcine Na /Ca2 exchanger.

Zoltán Macháty, Jagdeece J. Ramsoondar, Aaron J. Bonk, Randall S. Prather, and Kenneth R. Bondioli "Na /Ca2 Exchanger in Porcine Oocytes," Biology of Reproduction 67(4), 1133-1139, (1 October 2002).
Received: 7 February 2002; Accepted: 1 May 2002; Published: 1 October 2002
gamete biology
oocyte development
signal transduction
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