Abstract
Coated membranes in two types of gill epithelial cell of adult lamprey, Lampetra japonica, were studied by electron microscopy. The type 3 gill epithelial cells possess well-developed microvilli or microfolds, apical vesicles and abundant mitochondria. The cytoplasmic surface of the microvillous plasma membrane is covered by a coat of regularly spaced particles with a center-to-center distance of about 15 nm. Each particle consists of a bulbous free end, about 10 nm in diameter, and a connecting piece, about 5 nm long. Apical vesicles are covered by a surface coat which consists of fine filamentous material but lack any special coating on their cytoplasmic surface. The type 4 cells (chloride cells) are characterized by apical vesicles, abundant mitochondria and cytoplasmic tubules. These tubules possess a coat on their luminal surface which consists of spirally wound parallel rows of electron-dense materials. The rows are about 16 nm apart and wound at a pitch of about 45 degrees. The cytoplasmic surface of these tubules does not display a special coat. These coated membranes are assumed to be the sites of active ion transport across the plasma membrane. In particular, particles in type 3 cells and linear coat materials in chloride cells may be either loci of transport enzymes or energy generating systems. Apical vesicles lack any coating on their cytoplasmic surface but a fine filamentous coat is present on their luminal surface. They contain "intraluminal vesicles" and are continuous with apical ends of cytoplasmic tubules.
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