Characterization of morphological and histochemical changes induced by overexpression of P-glycoprotein in mouse leukemic cell line L1210.

Vincristine sensitive (L1210) and resistant (L1210/VCR) L1210 mouse leukemia cells were studied from morphological and histochemical point of view. The morphological and histochemical findings reflected differences in membrane structure and in physiological state of sensitive and resistant cells. Numerous villous projections and cytoplasmic protrusions of the cell surface as well as higher activity of membrane enzymes (5'-nucleotidase, ATPase, alkaline phosphatase) were found in vincristine resistant cells. It is assumed that in resistant cells these differences are connected with overexpression of membrane P-glycoprotein. Moreover, in resistant cells more condensed mitochondria were found after their exposure to vincristine. This finding can reflect a higher activity of these organelles in conditions when activity of P-glycoprotein is manifested and is in agreement with increased rate of oxygen consumption by resistant cells from 2.5 +/- 0.3 to 3.3 +/- 0.2 microliter/min.10(6) cells induced by vincristine.