Studies on Ca2+-stimulated adenosine triphosphatase in rat submandibular glands: its distribution and properties

Inhibitory effect of sulfhydryl group on Ca(2+)-ATPase activity in the plasma membrane-rich fraction from bovine parotid gland

1. The present study demonstrated that the Ca(2+)-ATPase activity of the plasma membrane-rich fraction from bovine parotid gland was decreased by the addition of reducing agents. 2. Ca(2+)-ATPase activity staining on SDS-PAGE gels was lost in the presence of 2-mercaptoethanol. 3. Among all the reducing agents tested, GSH was the most effective in inhibiting Ca(2+)-ATPase. 4. The Ca(2+)-ATPase activity decreased by the GSH was restored by the addition of an oxidizing reagent. However, oxidation with an oxidizing reagent subsequent to alkylation of the reduced enzyme with iodoacetamide resulted in no restoration of activity. 5. The decrease of Ca(2+)-ATPase activity by GSH is due to a decrease in the Vmax of the enzyme. 6. These results suggest that the disulfide bond in this enzyme protein is necessary to maintain the activity of this enzyme.

Characterization of Ca(2+)-ATPase of Setaria cervi (Nematoda: Filarioidea): effect of phenothiazines and anthelmintics

1. A Mg2+ independent, Ca(2+)-ATPase requiring high concentrations of Ca2+ (5 mM) for the activation, equally distributed in cuticle-muscular-hypodermis, genital organs and gastrointestinal tissues and mainly localized in 10,000 g pellet fraction, was identified in Setaria cervi, a bovine filarial parasite. 2. Filarial enzyme showed Km value of 3.33 mM for ATP as computed from the double reciprocal Lineweaver-Burk plot. 3. The enzyme could be completely solubilized by sonication with about 4-fold increase in specific activity of the enzyme. 4. The enzyme showed about 2-fold activation by the calmodulin fractions isolated from S. cervi and rat brain homogenates. 5. The enzyme was highly sensitive to inhibition with some phenothiazine derivatives. Trifluoperazine was observed to be the most potent inhibitor followed by promethazine and chlorpromazine. 6. Some anthelmintics viz. diethycarbamazine and centperazine were found to be highly potent inhibitors of the enzyme, significant inhibition of filarial Ca(2+)-ATPase was also observed with levamisole and suramine. 7. Studies indicate Ca(2+)-ATPase of S. cervi as a potential chemotherapeutic target.

Effect of dietary essential fatty acid deficiency on Ca(2+)-ATPase activity in microsomal fraction of rat submandibular gland

1. The effect of dietary essential fatty acid (EFA) deficiency on Ca(2+)-ATPase activity of rat submandibular gland microsomal fraction was studied. 2. The specific activity of Ca(2+)-ATPase per milligram of microsomal protein was depressed about 35% in rats fed the EFA-deficient diet as compared with that in those fed the control diet. 3. Lineweaver-Burk plots for Ca(2+)-ATPase activity showed no significant differences in Km values for Ca2+ and ATP, but the Vmax was decreased in the EFA-deficient rats. 4. The above results suggest that depression of the Ca(2+)-ATPase activity in rats fed the EFA-deficient diet is probably due to the decrease in the Vmax of the enzyme.

Separation of Ca2(+)-ATPase from Mg2(+)-ATPase in plasma membrane-rich fraction of bovine parotid gland

Ca2(+)-ATPase, which does not require Mg2+ for its activation, was separated from Mg2(+)-ATPase by papain treatment of a membrane-rich fraction of bovine parotid gland. The enzyme was partially purified 48-fold by subsequent chromatography on DEAE-cellulose, gel filtration on HPLC, and ion-exchange HPLC. The enzyme showed a molecular weight of 100,000, as estimated by gel filtration on HPLC. The Ca2(+)-ATPase was activated by Ca2+ but not by Mg2+, and this enzyme did not require Mg2+ for its activation by Ca2+. In fact, Mg2+ was inhibitory. p-Nitrophenyl phosphate was not hydrolyzed in the presence of Ca2+ or Mg2+, and this enzyme had no activities of other phosphatases tested. These results suggest that the Ca2(+)-ATPase is a separate enzyme from Mg2(+)-ATPase, Ca2(+)-stimulated Mg2(+)-dependent ATPase, and alkaline phosphatase, all of which are well known to be present in other tissues.

Characterization of the kinetic and regulatory properties of high-affinity Ca2+-ATPase activity in acinar preparations of rat submandibular salivary glands

High-affinity Ca2+-ATPase activity was characterized in the total particulate fraction of acinar preparations from rat submandibular glands. The Ca2+ concentration (as Ca2+-ATP) at half of maximal activity was 82 +/- 17 nM, the Hill coefficient was 2.36 +/- 0.6 and activity reached a steady level at approximately 200 pmol Pi min-1 microgram of membrane protein-1 from 1 to 20 microM Ca2+-ATP. High-affinity Ca2+-ATPase required micromolar concentrations of Mg2+ and was inhibited approximately 60 per cent by the phenothiazine derivative, fluphenazine, but was unaffected by ouabain, Na+, K+, La3+, ruthenium red, oligomycin and added calmodulin. Kinetics of adenosine diphosphate, guanosine triphosphate, uridine triphosphate and inosine triphosphate hydrolysis were similar to those of Ca2+-ATP but p-nitrophenylphosphate was a poor substrate. In the heavy microsomal fraction of whole glands, active Ca2+ uptake (ATP-dependent, oxalate-enhanced and abolished by A23187) was measurable in the absence of added Mg2+, was inhibited by fluphenazine and was stimulated by submicromolar concentrations of Ca2+-ATP. Thus rat submandibular glands contain the enzymic basis of active Ca2+ transport and can actively transport Ca2+. Both activities are stimulated at Ca2+ concentrations typical of the cytosol, appear to be positively cooperative and may be regulated, in part, by calmodulin.

Correlation between Ca2+-stimulated adenosine triphosphatase activity and Ca2+ uptake in microsomal fraction of rat submandibular gland

Both the Ca2+-ATPase activity and the Ca2+ uptake in a microsomal fraction of rat submandibular gland were inhibited by the addition of indomethacin in vitro. The decrease of both the Ca2+-ATPase activity and the Ca2+ uptake caused by the drug closely paralleled each other (r = 0.97). The inhibitory manner of indomethacin on Ca2+-ATPase and Ca2+ uptake was noncompetitive for Ca2+. These results suggest that the Ca2+-ATPase in the microsomal fraction of rat submandibular gland is a Ca2+ pump in this tissue.

Effect of phospholipase A2 on Ca2+-stimulated adenosine triphosphatase activity in microsomal fraction of rat submandibular gland

The effect of phospholipase A2 on the Ca2+-ATPase (EC 3.6.1.3) activity in the microsomal fraction of rat submandibular gland was kinetically studied in vitro. The Ca2+-ATPase activity was significantly increased by the treatment with phospholipase A2 in the presence of bovine serum albumin as a scavenger for hydrolyzed products. When the microsomal fraction was incubated with phospholipase A2 in the absence of bovine serum albumin, the Ca2+-ATPase activity was not altered. The Vmax and Km values for both ATP and Ca2+ were increased by the phospholipase A2 treatment, respectively. These results indicated that the activation of Ca2+-ATPase by the phospholipase A2 treatment is due to the increase of Vmax.

Cytochemical localization of ouabain-sensitive, K+ -dependent p-nitrophenylphosphatase and Ca++-stimulated adenosine triphosphatase activities in human parotid and submandibular glands

K+ -dependent p-nitrophenylphosphatase (pNPPase) and Ca++ -stimulated adenosine triphosphatase (ATPase) activities were studied in human parotid and submandibular glands using cytochemical methods at the ultrastructural level. In both glands, only the striated-duct epithelium showed K+ -pNPPase reaction product, thereby indicating the localization of Na+, K+ -ATPase. The precipitate was concentrated on the deep invaginations of the basolateral plasma membranes, in close association with their cytoplasmic surface. Ca++ -ATPase activity was also found on the basolateral plasma membranes, but two striking differences from the K+ -pNPPase distribution were observed: firstly, Ca++ -ATPase appeared in both acinar and ductal cells, and secondly, it was localized on the outer side of the plasma membranes.

Vitamin D-mediated decrease of Ca2+-pump activity in the rat parotid gland

In vitro activities of Ca2+-ATPase and 45Ca2+ uptake in microsomes, which were prepared from vitamin D-deficient rat parotid glands, were decreased in parallel by the oral administration of vitamin D3 as compared with those of control animals (r = 0.83). In vivo 45Ca2+ uptake in the parotid glands of vitamin D-deficient rats was also decreased by the oral administration of vitamin D3.

Effect of pyridoxal 5'-phosphate on Ca2+-stimulated adenosine triphosphatase activity in microsomes of rat submandibular gland in vitro

1. The Ca2+-ATPase activity in microsomes of rat submandibular gland was inhibited by pyridoxal 5'-phosphate in vitro. 2. The dissociation constant of the enzyme-pyridoxal 5'-phosphate complex was estimated to be 6.5 mM. 3. The inhibition of pyridoxal 5'-phosphate for both ATP and Ca2+ was competitive. 4. The order of inhibitory effectiveness of pyridoxal 5'-phosphate analogs was pyridoxal 5'-phosphate greater than pyridoxal HCl greater than pyridoxamine 5'-phosphate greater than pyridoxamine HCl. 5. The enzyme-pyridoxal 5'-phosphate complex was nonreducible with sodium borohydride.

Effect of indomethacin on Ca2+-stimulated adenosine triphosphatase in the synaptic vesicles of rat brain in vitro

1. Indomethacin inhibits calcium-stimulated adenosine triphosphatase (Ca2+-ATPase), calcium, magnesium-stimulated adenosine triphosphatase (Ca2+,Mg2+-ATPase) and magnesium-stimulated adenosine triphosphatase (Mg2+-ATPase) activities in rat brain synaptic vesicles in vitro. 2. The Ca2+-ATPase activity is most strongly affected by this drug all of the activities of ATPases tested. 3. The decrease of Ca2+-ATPase activity by addition of indomethacin is due to a decrease of Vmax. 4. The Ki values for this drug for ATP and Ca2+ in Ca2+-ATPase were 1.13 mM and 0.68 mM, respectively.

Effect of indomethacin on Ca2+-stimulated adenosine triphosphatase in the microsomes of rat submandibular gland

The effect of indomethacin, which is a nonsteroidal anti-inflammatory drug, on Ca2+-stimulated adenosine triphosphatase (Ca2+-ATPase) activity in the microsomes of rat submandibular gland was investigated. The effect of aspirin on Ca2+-ATPase activity was also studied.

Studies on calcium-stimulated adenosine triphosphatase in the albino rabbit dental pulp. Its subcellular distribution and properties

The subcellular distribution of calcium-stimulated adenosine triphosphatase in the albino rabbit dental pulp was studied. The purity of the microsomal fraction was examined by measuring the marker enzymes and by electron microscopic observation. Some properties of calcium-stimulated adenosine triphosphatase were investigated.

Developmental changes of calcium-stimulated adenosine triphosphatase in rat submandibular gland

Developmental changes in Ca2-+ ATPase activity were determined in submandibular glands of the rat from the fetus to the 300-day-old rat. Ca2+-ATPase in the homogenate fraction showed a rapid increase from the fetus to the 5-day-old rat, and from the 20- to 30-day-old rat. In the microsomal fraction, enzyme activity increased from the fetus to the 10-day-old rat, and after that is remained at almost the same level. Oscillatory phenomena of Ca2+-ATPase were observed in zymogen and mitochondrial fractions.