Dexniguldipine hydrochloride, a protein-kinase-C-specific inhibitor, affects the cell cycle, differentiation, P-glycoprotein levels, and nuclear protein phosphorylation in Friend erythroleukemia cells.

Dexniguldipine hydrochloride (DNIG) is a potent antineoplastic agent with well-documented anti-(protein kinase C) activity and an ability to reverse multidrug resistance. Given the importance of protein kinase C (PKC) activity in proliferation and differentiation, we examined the effect of DNIG on several parameters of Friend erythroleukemia cell (FELC) activity. Particular attention was paid to proliferation, hexamethylene-bisacetamide-(HMBA)-induced differentiation, nuclear localization of protein kinase C, and nuclear protein phosphorylation. P-glycoprotein expression was also followed as an indicator of changes in multidrug resistance. At 2.5 microM, DNIG caused a significant decrease in the rate of FELC proliferation, while maintaining a cellular viability of greater than 80%, whether exposure to the drug was continuous over 96 h or took the form of a 6-h pulse/chase. DNA synthesis was decreased in cells exposed to DNIG for 20 h. Flow cytometry showed a marked increase in the percentage of cells in S phase of the cell cycle. Phosphorylation studies revealed decreased phosphorylation of two nuclear proteins (80 kDa and 47 kDa) following a 4-h exposure to the drug. HMBA-induced differentiation was significantly inhibited with continuous exposure to DNIG, and this effect appears to be a pre-commitment one, as 6-h pulse/chase exposures also resulted in inhibition of differentiation. Cells induced to differentiate with HMBA also demonstrated a decrease in the quantity of the 80-kDa phosphoprotein. Western blotting revealed that, even in the face of decreased phosphorylation, exposure to this PKC inhibitor resulted in an increase in the amount of nuclear PKC alpha. Finally, levels of P-glycoprotein were decreased in the presence of this drug. Our work identifies several effects of the PKC inhibitor DNIG on FELC and suggests several roles for PKC in regulating FELC proliferation and differentiation. Additionally, these results suggest that this PKC inhibitor may increase the effect of other chemotherapeutic drugs, particularly S-phase-specific ones, by increasing the length of S phase and decreasing multidrug resistance. The possibility of combination therapy with DNIG and other antineoplastic agents should be investigated further in light of these findings.

A positional discriminability model of linear-order judgments.

The process of judging the relative order of stimuli in a visual array was investigated in three experiments. In the basic paradigm, a linear array of six colored lines was presented briefly, and subject decided which of two target lines was the leftmost or rightmost (Experiment 1). The target lines appeared in all possible combinations of serial positions and reaction time (RT) was measured. Distance and semantic congruity effects were obtained, as well as a bowed serial position function. The RT pattern resembled that observed in comparable studies with memorized linear orderings. The serial position function was flattened when the background lines were homogeneously dissimilar to the target lines (Experiment 2). Both a distance effect and bowed serial position functions were obtained when subjects judged which of two target lines was below a black bar cue (Experiment 3). The results favored and analog positional discriminability model over a serial ends-inward scanning model. The positional discriminability model was proposed as a "core model" for the processes involved in judging relative order or magnitude in the domains of memory and perception.