Stimulation of Calcium Influx in HL60 Cells by Cholesteryl-Modified Homopolymer Oligodeoxynucleotides

Abstract

Cholesteryl-modified 15-mer homopolymers of cytidine and thymidine phosphodiester oligodeoxynucleotides (chol-OdC15 and chol-OdT15), but not chol-modified heteropolymeric oligos or cholmodified phosphorothioate oligos, were found to increase cytosolic free Ca²⁺ in HL60 cells. A flow cytometer and the calcium-sensitive dye indo-1 were used to make multiparameter measurements on the HL60 cells. Chol-OdC15 (5-10 μM) triggered a rapid increase (within 1 min) in [Ca²⁺] _i , with a subsequent slow decline to baseline over 15 min in the continuous presence of agonist. The effect was preserved after unloading the intracellular Ca²⁺ stores with caffeine and ryanodine. The effect was not sensitive to membrane depolarization by KC1 (60 mM) or nimodipine, a dihydropyridine calcium channel antagonist. An increase in [Ca²⁺] _i was absent in a Ca²⁺-free solution and was inhibited by the inorganic Ca²⁺ channel blocker Cd²⁺. The results suggest that Ca²⁺ influx activated by the chol-oligomer is probably mediated by receptor-operated Ca²⁺ channels. This effect may be due to direct binding of the chol-oligo to the channel or to induced conformational changes due to modification of the local microenvironment.