Fig. 4.

Cellular and molecular elements underlying rod osmotic swelling. (A) Rod schematic (cyan) overlaid on a micrograph of a plastic section of a mouse retina. (B) Electron micrograph of the base of a mouse rod OS from the classic study of Carter-Dawson and LaVail, reprinted with permission from ref. 61. (C) Structural model of 20-nm × 20-nm patches of two pairs of adjacent disc bilayers in a dark-adapted rod OS, identified in B. Illustrated are rhodopsins (purple, eight per patch, corresponding to 25,000 μm⁻²), two heterotrimers (Gα_t, blue; Gβ₁ green; Gγ₁, red), and one phosphodiesterase (cyan). The disc-to-disc spacing was set to 32 nm (Materials and Methods). (D) Molecular-scale consequences of osmotic swelling: The interdiscal cytoplasmic space is stretched by ∼20%, and the G-protein heterotrimers are dissociated into Gα_t and Gβ₁γ₁ components and solubilized. ELM, external limiting membrane; ONL, outer nuclear; OPL, outer plexiform.