The samples were rapidly frozen at −210 °C using a JFD-380P slushy nitrogen production device (JEOL Ltd., Japan). Freeze fracture replica preparations were obtained by making reference to the method described by Buchheim [6] using JFD-9010 freeze etching equipment (JEOL Ltd., Japan). The samples were fractured at −165 °C, shadowed with 2 nm of platinum/carbon under an angle of 45°, and coated with 20 nm of carbon. The replicas were cleaned in concentrated sodium hypochlorite and distilled water. All samples were examined with a H-9000NA transmission electron microscope (Hitachi Ltd., Japan) operating at 100 kV accelerating voltage.