Effect of copper on isolated rabbit blastocysts

The effect of copper on the electrical membrane properties of the isolated-perfused 6-day rabbit blastocyst was studied to understand changes in the intrauterine environment caused by the copper IUD. Blastocysts were perfused in an environmental chamber containing Krebs-Ringer bicarbonate with 1 mg bovine serum albumin/ml. Electrical measurements made included short-circuit current (SCC) (the net result of currents produced by all net active ionic transport processes when there is no electrochemical gradient), transmural potential difference (p.d.), and conductance (computed from the ratio of open circuit p.d. to SCC). Control values were obtained and 9 experiments were performed in which 10 mcl aliquots of ?cuCl2 was added to the bathing solution. Electrical parameters of solutions containing 10-5M concentration CuCl2 remained essentially unchanged. 2.5 x 10-5 M reduced average p.d. 25% and average SCC 12%, WHILE 5 X 10-4C-5 M further reduced p.d. 48% and SCC 38% after 30 minutes. At 7.5 x 10-5 M p.d. was depressed 89% after 10 minutes with 1/3 of the values being positive, and SCC values decreased to 71% at 10 minutes and then increased to 77% of control values at 30 minutes. The subsequent changes in p.d. and SCC caused a 6-fold increase in membrane conductance. 9 experiments were performed on a 2nd group of blastocysts in which the effects of a single addition of CuCl2 at 10-4 M were studied. Average p.d. decreased reversing to positive values at 30 minutes. There was a biphasic response to SCC decreasing to 46% after 20 minutes then increasing to 1.7 times control values. Single additions of copper ions collapsed all blastocysts after a return to copper-free solutions. Serial additions showed only 3 out of 9 collapsing under similar conditions. Further experiments involving simultaneous SCC-isotope flux are necessary to determine which specific actively transported ions are affected by copper and to determine the effect on conductance. It is suggested that the action of copper in these experiments might have some bearing on the effectiveness of the copper IUD.