mitoguazone and 2-aminoisobutyric-acid

Studies were carried out to determine the possible roles of the polyamines, cyclic nucleotides, icosanoid products, and protein kinase C in the prolactin regulation of amino acid transport in cultured mammary gland explants derived from 12-14 day pregnant mice. Elevated cyclic AMP concentrations impaired the PRL stimulation of AIB transport. DBcAMP as well as the phosphodiesterase inhibitors theophylline and methyl isobutylxanthine, when added to the cultures, attenuated or abolished the PRL responses. 8-Bromo cyclic GMP elicited a modest stimulation of AIB transport. Ongoing polyamine synthesis appears to be necessary for PRL to effect a stimulation of AIB transport since methylglyoxal bis(guanyl hydrazone), an inhibitor of S-adenosyl methionine decarboxylase, abolishes the PRL response; specificity of this effect was established by its reversal with the addition of spermidine to the culture medium. Ongoing icosanoid product synthesis also appears to be required for the PRL stimulation of AIB transport since indomethacin abolishes the PRL response. Finally, the inhibition of the PRL response by the protein kinase C inhibitor H-7 suggests that the activation of kinase C activity may also be involved in the PRL stimulation of AIB transport.

Topics: 1-Methyl-3-isobutylxanthine; Aminoisobutyric Acids; Animals; Biogenic Polyamines; Bucladesine; Cells, Cultured; Eflornithine; Enzyme Activation; Female; Indomethacin; Mammary Glands, Animal; Mice; Mitoguazone; Nucleotides, Cyclic; Phosphodiesterase Inhibitors; Prolactin; Prostaglandins; Protein Kinase C; Spermidine

The transport pathway for the polyamine spermidine (SPD) was characterized in primary isolates of type II pulmonary epithelial cells from rat lungs. [14C]spermidine was accumulated by type II cells via a temperature-, sodium-, and concentration-dependent saturable pathway, with an apparent Km of 0.48 microM and a maximum velocity (V max) of 0.32 pmol.microgram DNA-1.min-1. SPD uptake was inhibited by gramicidin and by reduced extracellular sodium but was unaffected by alpha-aminoisobutyric acid (AIB), which entered the cells by a similar saturable pathway. Uptake of SPD also was inhibited by the exogenous polyamines putrescine (PUTR) and spermine (SPM), as well as by the methylglyoxal bis(guanylhydrazone) (MGBG) and by paraquat (PQ). The order of potency of these inhibitors was SPM greater than PUTR = MGBG much greater than PQ. The absence of serum reduced the Vmax of the system slightly but had no effect on the apparent Km. In contrast, after 3 days in primary cell culture, the kinetics of SPD transport were altered by decreases in both the Km and Vmax of the uptake process. These observations indicate that type II pulmonary epithelial cells exhibit a pathway of polyamine uptake with general characteristics similar to those observed previously in intact lung tissue and other cell types.

Topics: Aminoisobutyric Acids; Animals; Biological Transport; Blood; Calcimycin; Cells, Cultured; Epithelium; Gramicidin; Kinetics; Lung; Male; Mitoguazone; Paraquat; Putrescine; Rats; Rats, Inbred Strains; Sodium; Spermidine; Spermine; Temperature

The uptake of polyamines, methylglyoxal bis(guanylhydrazone) (MGBG), and paraquat [N,N-dimethyl-4,4'-bipyridylium] into control Chinese hamster ovary (CHO) cells and a mutant CHO cell line selected for resistance to the toxicity of MGBG was examined. In contrast to control CHO cells, the mutant cells had no detectable uptake of MGBG or any of the polyamines. There was no difference between the two cell lines in the uptake of alpha-aminoisobutyric acid (AIB), which indicates that there was no general change in membrane transport processes. The mutant cells were also found to be resistant to the toxicity of paraquat and to have a reduced capability to take up the herbicide. This finding confirms that the uptake of paraquat is necessary for the toxicity of this compound and that the paraquat is taken up by a transport system that also transports MGBG. Competition experiments showed that an excess of unlabeled paraquat inhibited uptake of MGBG and, to a lesser extent, uptake of putrescine and spermidine, but no inhibitory action on spermine uptake could be detected. Studies with type II cells isolated from rat lung also demonstrated uptake of paraquat and spermidine, but paraquat was only a weak inhibitor of spermidine uptake in this system. These results suggest that there may be multiple systems for the uptake of MGBG and polyamines and that paraquat is taken up by at least one but not by all of these systems.

Topics: Aminoisobutyric Acids; Animals; Cricetinae; Cricetulus; Dose-Response Relationship, Drug; Eflornithine; Female; Mitoguazone; Ovary; Paraquat; Polyamines; Putrescine; Spermidine; Spermine