Delta and sigma sites of clonal NCB20 cells do not modulate calcium uptake

Opiate alkaloids and peptides are reported to inhibit ⁴⁵Ca²⁺ binding to synaptic plasma membranes and uptake into brain synaptosomes. We have examined the effects of a number of opiates on ⁴⁵Ca²⁺ uptake in a clonal cell line NCB20 which expresses multiple opioid binding sites. The cells express voltage-dependent calcium channels that are blocked by verapamil and nifedipine. In contrast to brain, ⁴⁵Ca²⁺ uptake in these cells, in normal or high potassium medium, is unaffected by opiates. This difference may be due to the particular receptor types; the δ and σ sites of these cells do not inhibit ⁴⁵Ca²⁺ uptake.