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Abstract: 39
Zoltán Macháty1 *, Nancy Ruddock1 , Randall Prather1 *
Department of Animal Sciences, University of Missouri, Columbia, MO. 1
Sodium/calcium exchange is a carrier-mediated transport process that couples the transmembrane movement of 3 sodium ions to that of 1 calcium ion in the opposite direction. It is mediated by the sodium/calcium exchanger whose primary function, under steady-state conditions, is to extrude calcium out of the cell. However, under special circumstances (e.g. high intracellular sodium levels or in the absence of extracellular sodium) it can also operate in reverse mode serving as a potential source for calcium influx. The aim of the present study was to investigate the presence of such an exchange mechanism in porcine oocytes.
In vitro matured porcine oocytes were loaded with the calcium indicator dye fura 2 and changes in the intracellular free calcium concentration ([Ca2+]i) were measured. Removal of extracellular sodium triggered reverse sodium/calcium exchange in 17 out of 20 oocytes, which was detected as an increase in [Ca2+]i. In 3 oocytes the elevation occurred as repetitive calcium transients. Inhibition of the sodium/potassium-ATPase with ouabain is known to increase intracellular sodium concentration; preincubation of the oocytes with 0.4 mM ouabain increased the sodium-dependent calcium influx. The [Ca2+]i elevation was totally abolished in the absence of extracellular calcium (n=9). Amiloride (1mM) that blocks the sodium/calcium exchanger, inhibited the calcium influx caused by the absence of extracellular sodium (n=7), while verapamil (50 µM) and pimozide (50 µM), inhibitors of L- and T-type voltage gated calcium channels, respectively, were without effect (n=18). These data indicate the presence of a sodium/calcium exchanger in porcine oocytes.
This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.