Figure 3.

Size distribution of P face particles in oocytes expressing AQP1, opsin, and Cx50. (A) In an oocyte expressing AQP1, there was a population of particles with a mean diameter of 8.9 ± 0.2 nm (N = 449) in addition to the endogenous particles. The particle density in this oocyte was 825 ± 63/μm² (n = 982). In oocytes expressing opsin, two particle populations occurred with similar frequency: 5.7 ± 0.3 nm (43%) and 6.8 ± 0.1 nm (57%) (N = 912). Particle density was 1,444 ± 43/μm² in this oocyte (n = 1,903). Cx50 particles had a mean diameter of 9.0 ± 0.3 nm (N = 411). The particle density in this oocyte was 1,415 ± 81/μm² (n = 1,763). The small population of apparently larger size (≈11 nm) in all of the above histograms corresponds to the population of larger endogenous particles (see Fig. 2). Cross-hatched regions correspond only to the 7.6-nm P face endogenous particles as confirmed by particle density determinations. (B) Relationship between the transmembrane domain cross-sectional area and the number of transmembrane α-helices. Freeze-fracture data for AQP1, opsin, and Cx50 (•) agree well with those from two-dimensional crystals of AQP1, opsin, and Cx43 (○) (1.40 ± 0.03 vs. 1.42 ± 0.05 nm²/helix).