Effects of gossypol on the activity of kidney (Na+ + K+)-ATPase and the functions of erythrocyte membrane.

ABSTRACT

Gossypol extracted from cottonseed oil, reputed to exert contraceptive action in males, may induce a side effect of hypokalemia. The cellular and molecular mechanisms by which gossypol produces hypokalemia are not quite understood. We have examined the inhibitory effect of gossypol on the activity of (Na+ + K+)-ATPase purified from the outer medulla of rabbit kidney, the half maximal inhibitory concentration (IC50) is 6.5 micron. The kinetic studies using this enzyme preparation show that gossypol is noncompetitive with ATP, Mg2+, Na+ and K+ with apparent Ki of 15.0, 13.0, 14.0 and 4.4 micron, respectively. On the other hand, in order to estimate the effects of gossypol on membrane transport of intact cells, we have investigated the effects of gossypol on the activity of (Na+ + K+)-ATPase, membrane integrity and permeability of human erythrocytes. It shows that gossypol inhibited the enzyme activity (greater than 5 micron) and expressed the hemolysis (greater than 50 micron) in vitro in a concentration-dependent manner, and increased the K+-efflux of the cells (10-40 micron). The above effects are antagonized by 1-2% bovine serum albumin. The data demonstrate that gossypol is a specific and potent membrane active agent. These results may be relevant to the in vivo actions of gossypol.

ABSTRACT

PIP Hypokalemia has been demonstrated to be the major side effect of gossypol administration for contraceptive purposes; however, the cellular and molecular mechanisms involved in this effect are unknown. This study investigated the effect of gossypol on the activity of (Na+ and K+)-ATPase purified from the rabbit kidney and the functions of erythrocyte membrane. Kinetic findings indicated gossypol is noncompetitive with ATP, Mg2+, Na+, and K+. On the other hand, gossypol inhibited the enzyme activity of (Na+ and K+)=ATPase, expressed the hemolysis in vitro in a concentration-dependent manner, and increased the K+ efflux of the cells. These effects were antagonized by 1-2% serum bovine albumin. These findings demonstrate that gossypol is a specific and potent membrane active agent capable of injuring the cell membrane.