Abstract
The ryanodine receptor/Ca 2+ release channels from skeletal (RyR1) and cardiac (RyR2) muscle cells exhibit different inactivation profiles by cytosolic Ca 2+. D3 is one of the divergent regions between RyR1 (amino acids (aa) 1872–1923) and RyR2 (aa 1852–1890) and may contain putative binding site(s) for Ca 2+-dependent inactivation of RyR. To test this possibility, we have deleted the D3 region from RyR1 (ΔD3-RyR1), residues 1038–3355 from RyR2 (Δ(1038–3355)-RyR2) and inserted the skeletal D3 into Δ(1038–3355)-RyR2 to generate sD3-RyR2. The channels formed by ΔD3-RyR1 and Δ(1038–3355)-RyR2 are resistant to inactivation by mM [Ca 2+], whereas the chimeric sD3-RyR2 channel exhibits significant inactivation at mM [Ca 2+]. The ΔD3-RyR1 channel retains its sensitivity to activation by caffeine, but is resistant to inactivation by Mg 2+. The data suggest that the skeletal D3 region is involved in the Ca 2+-dependent regulation of the RyR1 channel.
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