The Ca2+ pump inhibitor, thapsigargin, inhibits root gravitropism in Arabidopsis thaliana

Thapsigargin, a specific inhibitor of most animal intracellular SERCA-type Ca2+ pumps present in the sarcoplasmic/endoplasmic reticulum, was originally isolated from the roots of the Mediterranean plant Thapsia gargancia L. Here, we demonstrate that this root-derived compound is capable of altering root gravitropism in Arabidopsis thaliana. Thapsigargin concentrations as low as 0.1 µM alter root gravitropism whereas under similar conditions cyclopiazonic acid does not. Furthermore, a fluorescently conjugated thapsigargin (BODIPY FL thapsigargin) suggests that target sites for thapsigargin are located in intracellular organelles in the root distal elongation zone and the root cap, regions known to regulate root gravitropism.

Lithium-induced inhibition of Na-K ATPase and Ca ATPase activities in rat brain synaptosome

To explore the action mechanism of lithium in the brain, the author investigated the effects of lithium on Na-K ATPase and Ca ATPase in rat brain synaptosomes prepared from forebrains by the method of Booth and Clark. The activities of Na-K ATPase and Ca ATPase were assayed by the level of inorganic phosphate liberated from the hydrolysis of ATP. Lithium at the optimum therapeutic concentration of 1 mM decreased the activity of Na-K ATPase from the control value of 19.08 +/- 0.29 to 18.27 +/- 0.10 micromoles Pi/mg protein/h and also reduced the activity of Ca ATPase from 6.38 +/- 0.12 to 5.64 +/- 0.12 micromoles Pi/mg protein/h. The decreased activity of Na-K ATPase will decrease the rate of Ca2+ efflux, probably via an Na-Ca exchange mechanism and will increase the rate of Ca2+ entry by the depolarization of nerve terminals. The reduced activity of Ca ATPase will result in the decreased efflux of Ca2+. As a Conclusion, it can be speculated that lithium elevates the intrasynaptosomal Ca2+ concentration via inhibition of the activities of Na-K ATPase and Ca ATPase, and this increased [Ca2+]i will cause the release of neurotransmitters and neurological effects of lithium.

Intracellular calcium homeostasis in Leishmania mexicana. Identification and characterization of a plasma membrane calmodulin-dependent Ca(2+)-ATPase

The intracellular Ca2+ concentration in different trypanosomatids is about 50 nanomolar, which concentration in different trypanosomatids is about 50 nanomolar, which is 4 orders of magnitude lower than in the extracellular milieu. This fact implies the existence of well developed mechanisms for the maintenance of such a high calcium gradient. In higher eukaryotics a number of different structures have been implicated in this function. Some of them are located in intracellular organelles, and others in the plasma membrane. Since intracellular organelles are limited by their storage capacity, long-term Ca2+ homeostasis resides solely in the plasma membrane. In higher eukaryotics, a calcium pump or Ca(2+)-ATPase located in the plasma membrane, because of its high Ca2+ affinity, has been proposed as the structure responsible for the maintenance of the cytoplasmic Ca2+ concentration at the submicromolar level. The presence of a Ca(2+)-ATPase in trypanosomatids has been debated. While some groups have reported its absence, others have reported the existence of an enzyme which is Mg(2+)-independent or even inhibited by Mg2+. On the other hand, in none of these reports any correlation was shown between the Ca(2+)-ATPase activity observed and the Ca2+ transport function attributed to this enzyme. We have previously shown that a calmodulin-stimulated Mg(2+)-dependent Ca(2+)-ATPase is present in the plasma membrane of Leishmania braziliensis and of Trypanosoma cruzi. Plasma membrane vesicles from these parasites are able to accumulate Ca2+ in the presence of the ATP-Mg complex. The similarities found between the kinetics parameters and other properties of the Ca(2+)-ATPase and the Ca2+ transport activity strongly suggest a common molecular entity. The stoichiometry calculated from these parameters approaches the 1:1 stoichiometry for Ca2+ and ATP, as reported for the Ca2+ pump from higher eukaryotic cells. In this report we show that plasma membrane vesicles from Leishmania mexicana possess a Ca(2+)-ATPase with characteristics which are similar to that reported by us for other trypanosomatids. Thus, the enzyme has a high Ca2+ affinity which is further increased upon addition of calmodulin. The maximal velocity is also increased by calmodulin...

Effect of anthelmintics and phenothiazines on adenosine 5'-triphosphatases of filarial parasite Setaria cervi.

S. cervi showed particulate bound Ca2+ ATPase and Na+,K(+)-ATPase activities while Mg2+ ATPase was detected in traces. ATPase of S. cervi was also differentiated from the nonspecific p-nitrophenyl phosphatase activity. Female parasite and microfilariae exhibited higher Ca2+ ATPase and Na+,K(+)-ATPase activities than the male adults and the enzyme Na+,K(+)-ATPase was mainly concentrated in the gastrointestinal tract of the filarial parasite. Na+,K(+)-ATPase of the filariid was ouabain-sensitive while Ca2(+)-ATPase activity was regulated by concentration of Ca2+ ions and inhibited by EGTA. Phenothiazines, viz. trifluoperazine, promethazine and chlorpromazine caused significant inhibition of Ca2+ ATPase and Na+,K(+)-ATPase. Diethylcarbamazine was a potent inhibitor of these ATPases. Mebendazole, levamisole and centperazine also caused significant inhibition of the ATPases indicating this enzyme system as a common target for the action of anthelmintic drugs.

Tannic acid as a marker for membrane sidedness of human red cell vesicles

Membrane sidedness of human eythrocytes was investigated in inside-out vesicles (IOV's), ghosts and intact cells by means of transmission electron microscopy (e.m.) after tannic acid fixation. No gross difference in appeearance of either membrane surface was observed when IOV's were subjected to conventional e.m. preparation. This included in addition to tannic acid, a double fixation with glutaraldehyde and osmium, followed by "en bloc" and thin section staining with uranyl acetate and lead citrate. By contrast, if IOV's were treated with a high EDTA concentration (2-5 mM) before tannic fixation, granular, electron-dense deposits were found on one of the surfaces. The presence of such a meterial was unaffected by neuraminidase treatment prior to the EDTA step. On the hand, red cells show no electron-dense deposits when exposed to EDTA (5 mM) unless they presented a light cytoplasm and an altered membrane appearance. Such a material was only observed on the inner membrane surface. Furthermore, a similar distribution of such deposits following EDTA treatment was also found in white ghosts before being induced to vesiculate. These results indicate that tannic acid can be employed as a marker for the cytoplasmic surface of the human erythrocyte membrane when used in combination with EDTA

Adenosine triphosphatase systems in genital tract of testosterone treated male adult monkeys.

Studies on the distribution of Na+, K+-dependent, Mg2+ dependent and Ca2+ dependent Adenosine Triphosphatase (ATP-ases) in the testes, epididymis, seminal vesicles and prostate glands of mature bonnet monkeys were carried out with and without Testosterone propionate (TP) treatment. Comparatively, the Ca2+ dependent ATP-ase was very active in the testes, caput and cauda epididymis and prostate of control animals. However, the Mg2+-dependent ATP-ase activity was predominant in the seminal vesicles. In all the genital tissues the Na+, K+ dependent ATP-ase exhibited low activity compared to other ATP-ase systems. On TP treatment at 1 mg/kg body wt. dose for 30 consecutive days to the second group of animals, all classes of ATP-ases drastically decreased in the testes, cauda epididymis, seminal vesicles and prostate. While in caput epididymis the Mg2+-dependent ATP-ase was stimulated, the Na+, K+-dependent ATP-ase was decreased both in the caput and corpus epididymis by the hormone treatment. The present study reveals the general inhibitory influence on the ATP-ase systems and thereby ionic transport after long term TP administration.