Resting histiocytes within the dermis and epidermis of the cichlid fish Pterophyllum scalare exhibit an unusual association between stacks of lamellar cisternae and tubular structures greater in diameter than ordinary microtubules (macrotubules) after treatment with 2 × 10(−4) M vinblastine. Macrotubules are found in the intercisternal spaces in a regular side-by-side orientation and extend the entire length of the cisternae. The lamellae seem to be formed as a result of increased membrane proliferation of the outer nuclear membrane; in some instances, cisternae have been observed to be continuous with the nuclear envelope. Since blebbing of the outer nuclear membrane is also observed in untreated histiocytes, lamellae formation is envisaged as hypertrophy of a normally occurring process. The association of lamellae with macrotubules possibly indicates a relationship between membranes and microtubule proteins.

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