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Vinblastine-induced ultrastructural transition of microtubular scaffoldings in the SV40-transformed 3T3 murine fibroblasts
Dominic Fan and Herbert G. Voelz

SV40-transformed 3T3 cells (SV3T3) treated with the antitubulin chemotherapeutic agent vinblastine exhibited ultrastructural alterations in their cellular microtubular scaffolding by electron microscopy. Apparent disappearance of the subcellular microtubules occurred after the cells were incubated with vinblastine at 10 μg/ml at 37°C for 8 hours. Typical cytoplasmic microtubular crystals were found with additional smooth membrane-limited vesicles. These vesicles mimic the differentiation cellular organelle called annulated lamellae. Microtubules were frequently seen associated with the Golgi apparatus and rough endoplasmic reticulum in the SV3T3 cells. These microtubules may contribute to transport of products between the Golgi and the rough endoplasmic reticulum. When treated with vinblastine, microtubular crystals were also observed between the Golgi and the rough endoplasmic reticulum. The size and numbers of cytoplasmic inclusions were increased in vinblastinetreated cells. In the SV3T3 cells, microtubules are determined by image analysis to be 230 A° in diameter with a subunit wall of 45 A° thick. These microtubules have a center-to-center space of 55.6 A° between the protofilaments. The skewed heterodimeric microtubular subunits are composed of disk-like structures of 45 A° in length, 30 A° in width, and 20 A° in thickness. The subunit center-to-center skewed angle is 40 degree. After the cells were treated with vinblastine, the microtubules undergo a transitional dissociation, and reassemble into ordered crystals. These transitional microtubules have an increased diameter of 350 A°, and a larger protofilament center-to-center space of 85 A°. These morphometric measurements indicated that there is a critical microtubule dissociation distance of 30 A°, exceeded which the typical microtubular ultrastructure may no longer exist.

Keywords: Microtubule, vinblastine, SV3T3, electron microscopy, microtubular crystal

Abbreviations: PBS, phosphate buffer saline; DMP 30, (2, 4, 6-dimethylaminomethyl phenol); Epon, Commercial name for epoxy resins.

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