Fig 6. Disruption of ER [Ca²⁺] homeostasis dysregulates type I collagen synthesis.

(A) Intracellular chain association assay to follow assembly of monomeric pro-α1(I) and pro-α2(I) chains into heterotrimeric procollagen molecules, α1(I)₂α2(I), at 20 minute intervals of a pulse-chase analysis. Unincorporated pro-α1(I) chains are present in proband cells approximately 20 minutes longer in P1 fibroblasts (P1 FB) and P2 (P2 OB) osteoblasts versus normal control fibroblasts and osteoblasts (C). (B) Steady-state cell layer (cell) and secreted (media) collagen from normal control (C) and proband fibroblasts (P1-P3, FB) and osteoblasts (P2, OB) analyzed by SDS-Urea PAGE. Both the α1(I) and α2(I) chains of type I collagen from proband cells demonstrate faster electrophoretic migration than normal control type I collagen alpha chains.