The differentiated PC12 cell neuronal model was used to determine the effect of trimethyltin (TMT) on protein kinase C (PKC). Cells treated with 5–20 µM TMT showed a partial and sustained PKC translocation within 30 min and persisted over a 24‐h period. TMT treatment was accompanied by a low level of PKC down‐regulation over 24 h, which was small compared with that produced by phorbol esters. Confocal imaging of differentiated PC12 cells showed that PKC translocates to the plasma membrane and the translocation is blocked by the PKC inhibitor chelerythrine (1 µM). Phorbol myristate‐induced PKC down‐regulation or inhibition with chelerythrine provided protection against TMT‐induced cytotoxicity. It was concluded that TMT‐induced PKC translocation and activation contribute to the cytotoxicity of TMT in differentiated PC12 cells.

No abstract

A rat cortical astrocyte preparation was used to investigate the effects of organotins on glutamate regulation by astrocytes. Exposure of astrocytes to low levels of organotins produced significant changes in two key components of glutamate homeostasis: glutamine synthetase (CS) activity and the high-affinity transport of L-glutamate. Trimethyltin (TMT), triethyltin (TET), and triphenyltin (TPT) exhibited differential abilities to reduce GS activity and glutamate uptake. Cultures incubated with 1 microM TET or TPT, but not TMT, exhibited a marked decrease in GS activity. Exposure to TET or TPT also produced a significant decrease in glutamate transport activity that was not observed with TMT. These declines in activity were not attributable to cell loss as measured by MTT reduction and lactate dehydrogenase (LDH) leakage. Since the loss of GS activity and transporter activity was not seen with acute organotin exposure, it is most likely attributable to a decreased presence of fully functioning protein. While the attenuation of GS and glutamate transporter activities by organotins does not match their pattern of neurotoxicity, the results indicate the potential for subtoxic concentrations of these compounds to increase extracellular glutamate and interact with other excitotoxic episodes.

On the basis of reports that astrocytes play an important role in the neurotoxicity of trimethyltin (TMT), we investigated the sensitivity of astrocytes to TMT and compared it to triethyltin (TET), a neurotoxic analog with a different in vivo specificity. The gliotoxicity of these two compounds was further compared to that of tributyltin (TBT) and triphenyltin (TPT), two purportedly nonneurotoxic organotin compounds. The time and concentration components of organotin toxicity were determined by measuring lactate dehydrogenase (LDH) release and formazan production from dimethylthiazolyldiphenyltetrazolium bromide (MTT). A TMT concentration of 100 micromol/L did not elevate extracellular LDH until 48 h after exposure, while signs of toxicity were not seen at 72 h for concentrations less than 10 micromol/L. Extracellular LDH activity increased 24 h after exposure to concentrations of TET, TBT, and TPT as low as 2.5 micromol/L. TMT was the only organotin to produce a delayed cytotoxicity, requiring both higher concentrations and more time to produce discernible toxicity. In contrast with TBT and TPT, the toxicity of the two neurotoxic organotins (TMT and TET) produced an early increase in MTT reduction. The distinct pattern of toxicity for TMT does not explain its selective in vivo toxicity, but the lack of sensitivity of astrocytes to this organotin also does not rule out more subtle changes in these cells that could disrupt normal glial/neuronal interactions.

The isolated, electrically-driven, guinea pig left atrium was used to study the ability of two perfluorocarbon emulsions to prevent anaerobic hypofunction in the myocardium. A 20% perfluorodecalin (PFD) emulsion maintained peak tension at 80% of aerated levels for more than 20 minutes. Emulsions of perfluorooctylbromide (PFOB) ranging from 25 to 100% produced a similar result, except that the 25% emulsion could not maintain contractions for the entire time period. Peak tension of atria bathed in K-H solution decreased to less than 50% over the same time period. Both 20% PFD and 100% PFOB maintained myocardial ATP levels at pre-hypoxic levels for at least twenty minutes after aeration was terminated. Unaerated atria, bathed in Krebs-Henseleit solution only, exhibited a significant decline in tissue ATP levels at this time. It appears that perfluorocarbon emulsions may delay oxygen desaturation and thereby protect cardiac tissue from ATP depletion and impaired cardiac function associated with hypoxia. This tissue preparation was found to be very useful for determining the efficacy of potential oxygen carriers.