RyR1 and RyR3 isoforms provide distinct intracellular Ca²⁺signals in HEK 293 cells Available to Purchase

Ryanodine receptors (RyRs) are expressed on the endoplasmic reticulum of many cells, where they form intracellular Ca²⁺-release channels that participate in the generation of intracellular Ca²⁺ signals. Here we report studies on the intracellular localisation and functional properties of transfected RyR1 or RyR3 channels in HEK 293 cells. Immunofluorescence studies indicated that both RyR1 and RyR3 did not form clusters but were homogeneously distributed throughout the endoplasmic reticulum. Ca²⁺ release experiments showed that transfected RyR1 and RyR3 channels responded to caffeine, although with different sensitivity,generating a global release of Ca²⁺ from the entire endoplasmic reticulum. However, video imaging and confocal microscopy analysis revealed that, in RyR3-expressing cells, local spontaneous Ca²⁺ release events were observed. No such spontaneous activity was observed in RyR1-expressing cells or in control cells. Interestingly, the spontaneous release events observed in RyR3-expressing cells were restricted to one or two regions of the endoplasmic reticulum, suggesting the formation of a further subcellular organisation of RyR3 in Ca²⁺ release units. These results demonstrate that different RyR isoforms can engage in the generation of distinct intracellular Ca²⁺ signals in HEK 293 cells.