Recent investigations have shown that calcium entry blockers enhance the effects of hypoxia on erythropoietin (Ep) production in vivo. To determine whether deprivation of calcium increases Ep production and/or release, studies were carried out to determine the effects of low levels of extracellular calcium on Ep (radioimmunoassay) secretion in human renal carcinoma cells in culture. Low extracellular calcium levels (0.3 mM) in culture medium significantly (P less than 0.01) enhanced Ep secretion (64-145% increase per day) by renal carcinoma cells in culture when compared with a concentration of 1.9 mM calcium in the control culture medium (23-68% increase per day) incubated for 24 h or more. A 53% increase per day in Ep secretion was also produced by the calmodulin inhibitor trifluoperazine. To determine whether the effects of low calcium levels on Ep production could be due to nonspecific leakage of large intracellular molecules caused by a permeabilization of the cell membrane, the effect of low calcium levels in the cultures of the renal carcinoma cells on lactate dehydrogenase release into the culture medium was studied. Low calcium concentrations failed to significantly enhance lactate dehydrogenase secretion by the renal carcinoma cells. In conclusion, our results indicate a possible involvement of the calcium ion and calmodulin in the biosynthetic pathway for Ep and that calcium may exert a suppressive effect on Ep production.
Role of endogenous prostaglandin E2 in erythropoietin production and dome formation by human renal carcinoma cells in culture.
