| Abstract: | The degradation of 125I-labelled low-density lipoproteins (LDL) in HeLa cells was significantly inhibited when the cells were incubated either with the calcium channel blocking agents D600 and verapamil, or with the lysosomotropic agent chloroquine. However, nifedipine, another blocker of Ca2+ channels, did not affect the degradation of 125I-labelled LDL. The association of 125I-labelled LDL with HeLa cells was increased in proportion to the concentration of D600, and 125I-labelled LDL was accumulated in lysosomal fractions as assessed by Percoll density gradient analysis. Some 80% of 125I-labelled LDL in lysosomes of HeLa cells treated with D600 was acid-insoluble. The rate of incorporation of 3H]acetate into digitonin-precipitable material was increased 4-fold in the cells treated with 40 micrograms/ml D600 compared with untreated cells, but that of 3H]mevalonate was not enhanced. About 8 h of preincubation of the cells with D600 or verapamil was required to inhibit the LDL degradation by 50% of the control activity. It was also found that the inhibitory action of D600 could be reversed by removal of D600 from the medium. The activities of lysosomal enzymes, cathepsin B, beta-hexosaminidase, and acid phosphatase, were significantly decreased when the cells were treated with D600 and chloroquine, but not with nifedipine. Blockers of Ca2+ channels which effect the activity of lysosomal enzymes, should be useful for the study of the lysosomal function. |
