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.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.