The differential effects of the carcinogen dimethylnitrosamine on isocitrate and 6-phosphogluconate metabolism in single intact cells
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Abstract:
A microspectrofluorimetric study is made of the influence of dimethylnitrosamine on NADP reduction, following sequential microinjections into the same L cell, of two substrates: (1) isocitrate, with activity of isocitrate dehydrogenase both in the extramitochondrial and intramitochondrial compartments, (2) 6-phosphogluconate, with activity of the dehydrogenase in the extramitochondrial compartment. In control L cells a two-step reduction of NAD(P) is obtained followed by relatively slow reoxidation. In the minutes which follow addition of carcinogen, e.g., dimethylnitrosamine, to the cell medium the isocitrate and 6-phosphogluconate-induced transient NADP reoxidation is decreased in magnitude compared to control, while the rate constant of NADPH reoxidation is considerably accelerated, possibly due to requirements at the level of the microsomal metabolizing system. Observation within the first hour of carcinogen addition suggest an interesting system for evaluating the immediate actions of carcinogens at extranuclear sites: i.e., a comparative study of NADP reduction-reoxidation rate constants via injection of substrates for extra- vs. intramitochondrial pathways.
Insights
Dimethylnitrosamine exposure alters nicotinamide adenine dinucleotide phosphate (NADP) reduction and reoxidation in L cells. Carcinogen exposure accelerates NADPH reoxidation, indicating rapid extranuclear effects.
Area of Science:
- Cell Biology
- Biochemistry
- Toxicology
Background:
- Nicotinamide adenine dinucleotide phosphate (NADP) plays a crucial role in cellular redox homeostasis.
- Dimethylnitrosamine is a known carcinogen with complex cellular effects.
- Understanding early cellular responses to carcinogens is vital for toxicological research.
Purpose of the Study:
- To investigate the impact of dimethylnitrosamine on NADP reduction and reoxidation dynamics in L cells.
- To assess the influence of carcinogen exposure on enzymatic activities within different cellular compartments.
- To establish a method for evaluating immediate extranuclear carcinogen effects.
Main Methods:
- Microspectrofluorimetry was employed to monitor NADP reduction and reoxidation.
- Sequential microinjections of isocitrate and 6-phosphogluconate were used as substrates.
- Enzyme activities of isocitrate dehydrogenase and 6-phosphogluconate dehydrogenase were studied in extramitochondrial and intramitochondrial compartments.
Main Results:
- Control L cells exhibited a two-step NAD(P) reduction followed by slow reoxidation.
- Dimethylnitrosamine exposure significantly decreased the magnitude of NADP reoxidation induced by both substrates.
- The rate constant of NADPH reoxidation was markedly accelerated following carcinogen addition.
Conclusions:
- Dimethylnitrosamine rapidly affects NADP metabolism at extranuclear sites.
- Accelerated NADPH reoxidation suggests increased cellular demands, potentially linked to microsomal metabolism.
- The study presents a novel system for evaluating the immediate extranuclear actions of carcinogens.