Expression of ryanodine receptors in human embryonic kidney (HEK293) cells

It has been shown previously that mobilization of caffeine-sensitive intracellular calcium (Ca-i(2+)) stores increased the release of amyloid P-peptide (AB) from transfected human embryonic kidney cells (HEK293) [Querfurth, Jiang, Geiger and Selkoe (1997) J. Neurochem. 69, 1580-1591]. The present study was to test the hypothesis that the caffeine/A beta responses were due to interactions with specific subtypes of ryanodine receptors (RyR) using [H-3]ryanodine receptor binding, epifluorescence imaging of Ca-i(2+), immunocytofluorescence, immunoprecipitation and PCR techniques. [H-3]Ryanodine bound to a single class of high-affinity caffeine-sensitive sites (K-d = 9.9 +/- 1.6 nM, B-max = 25+/-4 fmol/mg of protein). RyRs were immune-decorated in a punctate reticulo-linear pattern. Results from SDS/PAGE and reverse transcriptase-PCR demonstrated endogenous expression of type 1 (skeletal) and type 2 (cardiac) RyRs, HEK293 cell RyRs were functionally active, because (i) [Ca2+](i) increased 2.8-fold over baseline following applications of 5-15 mM caffeine, (ii) repetitive spiked increases in [Ca2+](i) were observed, and (iii) evidence for a use-dependent block was obtained. Some of these findings were extended to include HeLa and human fibroblast cell lines, suggesting a broader applicability to cells of epithelioid lineage. Implications for the processing of the beta-amyloid precursor protein in Alzheimer's disease and for calcium channel research using transfected HEK293 cells are discussed.