Effects of cyclodiene compounds on calcium pump activity in rat brain and heart.

The in vitro and in vivo effects of aldrin, dieldrin, and endrin on calmodulin regulated Ca2+-pump activity in rat brain synaptosomes and heart sarcoplasmic reticulum were investigated. All the 3 cyclodiene compounds inhibited both brain synaptosomal and heart sarcoplasmic reticulum Ca2+-pump activity in vitro in a concentration dependent manner. Calmodulin depleted Ca2+-pump activity was insensitive to the action of toxic compounds. Oral administration of pesticides (0.5-10 mg/kg) to rats similarly decreased the Ca2+-pump activity, in addition to decreasing the levels of calmodulin of both brain and heart thus indicating disruption in membrane Ca2+ transport mechanisms. Exogenous addition of calmodulin (1-20 micrograms) could effectively reverse the pesticide induced inhibition. Ca2+-pump activity is more sensitive to the 3 cyclodiene compounds in brain than in heart. The results of the present study indicate that the cyclodiene compounds may produce neurotoxic effects by altering calmodulin regulated calcium dependent events in neurons.

Inhibition of calmodulin activated adenylate cyclase in rat brain by selected insecticides.

Effect of various insecticides on basal and calmodulin (CaM) activated adenylate cyclase activity was studied in solubilized rat brain nuclear and P2 fractions. Our earlier experiments indicated that plictran, chlordecone and other insecticides affect the calcium transport across cell membranes. The present experiments were designed with the assumption that these compounds might exert their neurotoxic action by interfering with CaM (a calcium receptor protein) regulated processes. We have used detergent solubilized adenylate cyclase for our studies, since membrane bound form is not sensitive to externally added CaM. CaM significantly elevated the adenylate cyclase activity in both the fractions and a maximum stimulation of 97% in nuclear fraction and 50% in P2 fraction was observed with 1 microgram of CaM. All the insecticides studied inhibited both basal and CaM activated adenylate cyclase activity in nuclear and P2 fractions to a different extent. A significant inhibition was observed at 0.05 microM and higher concentrations of plictran. Chlordecone and toxaphene inhibited both basal and CaM activated adenylate cyclase in a concentration dependent manner. Although dieldrin and aldrin inhibited basal adenylate cyclase in a concentration dependent manner, they did not exhibit a similar pattern on CaM activated adenylate cyclase. Of all the insecticides studies, chlordecone is more potent in inhibiting both basal and CaM activated adenylate cyclase which is in agreement with the greater neurotoxic action of this compound. These results indicate that all the insecticides studied are potent inhibitors of detergent solubilized adenylate cyclase, and might exert their neurotoxic differential action by interfering with CaM regulated events in central nervous system.

Effect of plictran on beef heart mitochondrial ATPases.

The in vitro effects of plictran on oligomycin-sensitive Mg2+-ATPase and Ca2+-ATPase activities in beef heart mitochondria were studied. Beef heart mitochondrial fractions were prepared by the conventional centrifugation method. ATPase activities were measured by determining the inorganic phosphate released by the hydrolysis of ATP. Plictran inhibited both oligomycin-sensitive (o.s.) Mg2+-ATPase and Ca2+ ATPase activities at nanomolar concentrations. However, plictran did not affect the oligomycin-insensitive (o.i.) Mg2+-ATPase activity at any concentration studied. Substrate activation kinetics revealed that plictran inhibited o.s. Mg2+-ATPase uncompetitively and Ca2+-ATPase non-competitively. These results clearly indicate that plictran affects ATP synthesis and calcium ion transport in beef heart mitochondria.

Rising levels of cardiovascular mortality in Mississippi, 1979-1995.

BACKGROUND: Cardiovascular disease rates are improving in the United States, but not for certain subgroups, especially some African Americans. The objective of the study is to assess current levels and trends in cardiovascular disease mortality in Mississippi. METHODS: Mortality statistics from the U.S. vital statistics system for the period 1979-95 were used. Comparison of age-adjusted mortality rates in Mississippi with the other states for the year 1995 and with the nation as a whole over the period of 1979-95 was performed. RESULTS: Mississippians had the highest age-adjusted cardiovascular disease morality rates in the nation in 1995. Overall, the cardiovascular rates in Mississippi were 37% higher than for the U.S. African American men and women from Mississippi had especially high cardiovascular mortality rates, approximately 50% and 70% higher than their white counterparts, respectively. The higher burden of cardiovascular disease in African Americans from Mississippi was especially marked in the younger age groups. Since about 1984-85, cardiovascular mortality rates in Mississippi have been increasing for African Americans, whereas nationally they have been decreasing. In contrast, cardiovascular mortality rates for whites in Mississippi have been declining, but at a much slower rate than seen nationally. The wide divergence in trends for African American and white men and women over that period in Mississippi has lead to an estimated 19,400 excess cardiovascular deaths. Virtually identical trends were found for heart disease. CONCLUSIONS: Cardiovascular diseases are a major public health problem in Mississippi that is especially severe in African American residents, and the problem is growing worse each year. It is important to identify the determinants of and solutions for this enormous public health problem in Mississippi.

Effect of subchronic dieldrin treatment on calmodulin-regulated Ca2+ pump activity in rat brain.

Calmodulin-dependent (CaM-dependent) and nondependent Ca2+ pump activity was determined in the brain P2 fraction of Sprague-Dawley rats treated in vivo with 10 ppm dieldrin for 60 d. After 40 d of dieldrin intoxication, daily food consumption and body weight gain were found to be affected. Dieldrin inhibited both CaM-dependent and -independent Ca2+-ATPase activity and the enzyme activity decreased to 36% (CaM-dependent)--and 18% (basal) respectively after 60 d of intoxication. Reduction in brain CaM levels and a subsequent inhibition of Ca2+-ATPase activity suggests that chronic intoxication of dieldrin at very low doses alters calmodulin and its regulation of Ca2+-ATPase activity.

Comparative effects of structurally related cyclodiene pesticides on ATPases.

Comparative effects of aldrin, dieldrin, endrin, isodrin and telodrin, on different ATPase activities in beef heart mitochondrial and rat brain synaptosomal fractions were determined in vitro. Beef heart mitochondrial fractions were prepared by the conventional centrifugation method and the rat brain synaptosomes were prepared by Ficoll-sucrose gradient centrifugation method. Na+-K+-ATPase, oligomycin-sensitive and -insensitive Mg2+-ATPases, and K+-paranitrophenylphosphatase were determined in rat brain synaptosomes. In beef heart mitochondria, only the Mg2+-ATPase activities were determined. Concentration response curves were determined by assaying the enzyme activities in the absence and presence of 10-120 microM concentrations of each test chemical. Beef heart mitochondrial (oligomycin-sensitive) Mg2+-ATPase activity was inhibited by all five chemicals at all the concentrations tested. Aldrin and telodrin were the most potent inhibitors with an IC50 of 40 and 80 microM, respectively. About 30% was observed with dieldrin, endrin and isodrin, and the inhibition was not concentration-dependent. Oligomycin-insensitive Mg2+-ATPase was not significantly inhibited by any chemical except aldrin. Rat brain synaptosomal ATPases were also sensitive to these compounds. Aldrin and telodrin were more effective than other compounds. A 50% inhibition of oligomycin-sensitive Mg2+-ATPase activity was obtained at 80 microM of aldrin and telodrin. Na+-K+-ATPase and oligomycin-insensitive Mg2+-ATPase activities showed a maximum inhibition of 40% at the highest concentration tested for aldrin and telodrin. K+-paranitrophenylphosphatase was not inhibited significantly by any compound tested. These results suggest that ATPase system in rat heart and CNS may be selectively inhibited by aldrin and telodrin, but not by their structural analogs.

Chlordecone interaction of calmodulin binding with phosphodiesterase.

The effects of organochlorine (O.C.) compounds, such as aldrin, dieldrin, endrin, isodrin, chlordecone and mirex, on calmodulin (CaM) activity were investigated. Changes induced by O.C. compounds on biological and physical properties of CaM were monitored in terms of phosphodiesterase stimulation and tyrosine fluorescence, respectively. None of the O.C. compounds altered tyrosine fluorescence of CaM in the presence of Ca2+. Except for chlordecone, none of the O.C. compounds inhibited CaM-activated phosphodiesterase (PDE). Chlordecone significantly decreased (P less than 0.05) CaM-activated PDE in a concentration-dependent manner without affecting the basal enzyme. Combination of chlordecone with W-7 (CaM antagonist) increased the inhibitory effect of W-7 on CaM activity. These results suggest that O.C. compounds may not be changing the tyrosine fluorescence of CaM. Among the O.C. compounds tested, chlordecone is a specific inhibitor of CaM-activated PDE.

Holothurin: an activator of bovine brain 3'-5' phosphodiesterase.

The effect of marine toxin, holothurin A, on calmodulin(CaM)-dependent bovine brain 3'-5' phosphodiesterase (PDE) was studied. Holothurin stimulated CaM-depleted PDE in a concentration dependent manner and this interaction was independent of Ca2+ concentrations. Activation of PDE by holothurin was pH and incubation temperature dependent. Heat treatment of holothurin (at 95 degrees C) at various time intervals (2-8 min) decreased its ability to stimulate PDE. CaM-dependent dependent PDE activity was decreased by holothurin. CaM antagonist W-7 and an organochlorine compound chlordecone significantly inhibited holothurin stimulated PDE. These data indicate that holothurin activates CaM-deficient 3'-5' PDE which is antagonized by classical CaM antagonists.

Sedimentation analysis of ribonucleotide reductase activity in extracts of Pseudomonas stutzeri.

Analysis of ribonucleotide reductase and DNA polymerase activities in extracts of Pseudomonas stutzeri by centrifugation in discontinuous sucrose gradients indicated that these two enzymes are associated with two different high molecular weight cellular components. In addition, 95% of the ribonucleotide reductase activity was pelleted by centrifugation of extracts for 4 hr at 200,000 X G. The reductase activity remained particulate (sedimentable) following sonication whereas some 90% of the DNA polymerase activity was rendered soluble (non-sedimentable) by this technique. This data indicate that the P. stutzeri ribonucleotide reductase is not a cytosolic enzyme, but is associated with a macromolecular component in the cell.

Effect of selected insecticides on rat brain synaptosomal adenylate cyclase and phosphodiesterase.

Previous reports from our laboratory and others clearly indicated that organochlorine insecticides such as chlordecone and DDT are potent inhibitors of ATPases involved in active ion transport. The present studies were initiated to study the effect of plictran, chlordecone, toxaphene, aldrin, dieldrin, endrin, isodrin, and telodrin on enzymes involved in cyclic AMP metabolism. Rat brain synaptosomes were prepared by Ficoll-sucrose gradient centrifugation method. Adenylate cyclase activity, which is involved in anabolism of cAMP, was determined using the radioactive method by measuring [32P]cAMP formed during hydrolysis of [32P]ATP. Phosphodiesterase activity, which is involved in the catabolism of cAMP, was estimated by measuring [3H]adenosine formed using [3H]cAMP as a substrate. Synaptosomal adenylate cyclase activity was inhibited significantly by plictran with an IC50 of 25 microM, and a maximum inhibition of 30% was observed with 50 microM chlordecone. Toxaphene, aldrin, dieldrin, endrin, isodrin, and telodrin did not affect the adenylate cyclase activity. Similarly, none of the insecticides studied inhibit the activity levels of synaptosomal phosphodiesterase. The significant inhibition of adenylate cyclase observed with plictran might be due to the tin component, since several heavy metals affect cAMP metabolism. The lack of inhibition of adenylate cyclase and phosphodiesterase with other compounds tested clearly supports our postulation that these organochlorine insecticides exert their neurotoxic action by the selective inhibition of ATPases in synaptosomes.