Inhibition of the human erythrocyte calcium pump by dimethyl sulfoxide

Supplementary cryoprotective effect of carboxylated ε-poly-l-lysine during vitrification of rat pancreatic islets

This study was designed to investigate whether cryosurvival of rat pancreatic islets can be improved by carboxylated ε-poly-l-lysine (CPLL). Islets isolated from Wistar × Brown-Norway F1 rats (101-200 μm in diameter) were cryopreserved in three vitrification solutions containing ethylene glycol (EG; 30%, v/v) and CPLL (0%, 10%, or 20%, v/v) by Cryotop^® protocol (10 islets per device). The post-warm survival rate of the islets vitrified in the presence of 20% CPLL (74%), assessed by FDA/PI double staining, was higher than those in 0% and 10% CPLL (65% and 66%, respectively). Decreased EG concentrations (10% and 20%) in the presence of 20% CPLL resulted in impaired post-warm islet survival rates (50% and 64%, respectively). Value of stimulus index (SI) for 20 mM/3 mM glucose-stimulated insulin secretion was 4.1 in islets vitrified-warmed in the presence of 30% EG and 20% CPLL, which was comparable with those in fresh control islets and vitrified islets in 30% EG alone (4.1 and 4.4, respectively). A large number of islets (50 islets per device) could be cryopreserved in the presence of 30% EG and 20% CPLL by using nylon mesh as the device, without considerable loss of post-warm survival (68%) and SI value (3.7). In conclusion, supplementation of antifreeze 20% CPLL was effective in improving the post-warm survival of isolated rat pancreatic islets when vitrification solution containing 30% EG was used.

Augmented behavioral response and enhanced synaptosomal calcium transport induced by repeated cocaine administration are decreased by calcium channel blockers

Recent studies suggest that calcium influx via L-type calcium channels is necessary for psychostimulant-induced behavioral sensitization. In addition, chronic amphetamine upregulates subtype Cav1.2-containing L-type calcium channels. In the present studies, we assessed the effect of calcium channel blockers (CCBs) on cocaine-induced behavioral sensitization and determined whether the functional activity of L-type calcium channels is altered after repeated cocaine administration. Rats were administered daily intraperitoneal injections of either flunarizine (40 mg/kg), diltiazem (40 mg/kg) or cocaine (20 mg/kg) and the combination of the CCBs and cocaine for 30 days. Motor activities were monitored on Day 1, and every 6th day during the 30-day treatment period. Daily cocaine administration produced increased locomotor activity. Maximal augmentation of behavioral response to repeated cocaine administration was observed on Day 18. Flunarizine pretreatment abolished the augmented behavioral response to repeated cocaine administration while diltiazem was less effective. Measurement of tissue monoamine levels on Day 18 revealed cocaine-induced increases in DA and 5-HT in the nucleus accumbens. By contrast to behavioral response, diltiazem was more effective in attenuating increases in monoamine levels than flunarizine. Cocaine administration for 18 days produced increases in calcium uptake in synaptosomes prepared from the nucleus accumbens and frontal cortex. Increases in calcium uptake were abolished by flunarizine and diltiazem pretreatment. Taken together, the augmented cocaine-induced behavioral response on Day 18 may be due to increased calcium uptake in the nucleus accumbens leading to increased dopamine (DA) and serotonin (5-HT) release. Flunarizine and diltiazem attenuated the behavioral response by decreasing calcium uptake and decreasing neurochemical release.

Alteration by EGTA of the human red cell Ca(2+)-ATPase

The effect of EGTA on Ca(2+)-ATPase activity was studied in fragmented membranes and solubilized preparations from human red cells. A dual action was found. At low concentrations (0.1-1 mM), EGTA increased Ca2+ affinity without affecting Vmax. By contrast, at high concentrations (5-10 mM), EGTA was inhibitory. Both effects were partially reversible.

Neutral organic solute effects on the activity of the plasma membrane Ca(2+)-ATPase

We have compared effects of dimethylsulfoxide (Me2SO) and two polyols on the Ca(2+)-ATPase purified from human erythrocytes. As studied under steady-state conditions over a broad solute concentration range and temperature, Me2SO, glycerol, and xylitol do not inhibit the Ca(2+)-ATPase activity; this is in contrast to numerous other organic solutes that we have investigated. Under specific experimental conditions, Me2SO (but not glycerol) substantially increases Ca(2+)-ATPase activity, suggesting a possible facilitation of enzyme oligomerization. The activation is more pronounced at low Ca2+ concentrations. In contrast to glycerol, Me2SO shows no protective effect on enzyme structure as assessed by determining residual Ca(2+)-ATPase activity after exposing the enzyme to thermal denaturation at 45 degrees C. Under these conditions several other organic solutes strongly enhance the denaturating effect of temperature. Because of the temperature dependence of its effect on the Ca(2+)-ATPase activity we believe that Me2SO activates the Ca(2+)-ATPase by indirect water-mediated interactions.

Activation of the human red cell calcium ATPase by calcium pretreatment

Some kinetic parameters of the human red cell Ca(2+)-ATPase were studied on calmodulin-free membrane fragments following preincubation at 37 degrees C. After 30 min treatment with EGTA (1 mM) plus dithioerythritol (1 mM), a Vmax of about 0.4 mumol Pi/mg x hr and a Ks of 0.3 microM Ca2+ were found. When Mg2+ (10 mM) or Ca2+ (10 microM) were also added during preincubation, Vmax, but not Ks was altered. Ca2+ was more effective than Mg2+, thus increasing Vmax to about 1.3 mumol P/mg x hr. The presence of both Ca2+ and Mg2+ during pretreatment decreased Ks to 0.15 microM, while having no apparent effect on Vmax. Conversely, addition of ATP (2 mM) with either Ca2+ or Ca2+ plus Mg2+ increased Vmax without affecting Ks. Preincubation with Ca2+ for periods longer than 30 min further increased Vmax and reduced Ks to levels as low as found with calmodulin treatment. The Ca2+ activation was not prevented by adding proteinase inhibitors (iodoacetamide, 10 mM; leupeptin, 200 microM; pepstatin A, 100 microM; phenylmethanesulfonyl fluoride, 100 microM). The electrophoretic pattern of membranes preincubated with or without Mg2+, Ca2+ or Ca2+ plus Mg2+ did not differ significantly from each other. Moreover, immunodetection of Ca(2+)-ATPase by means of polyclonal antibodies revealed no mobility change after the various treatments. The above stimulation was not altered by neomycin (200 microM), washing with EGTA (5 mM) or by both incubating and washing with delipidized serum albumin (1 mg/ml), or omitting dithioerythritol from the preincubation medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic activation of the human red cell calcium ATPase by magnesium and vanadate

The Ca(2+)-ATPase activity of human red cells was studied on calmodulin-free membrane fragments after previous incubation with Mg2+ and vanadate. In the presence of EGTA (5 mM), the activity was slightly affected by either ion alone. However, when added together, both Ca2+ affinity and Vmax were increased up to levels found with calmodulin (0.3 microM). This synergistic activation was not abolished by proteinase inhibitors (iodoacetamide, 10 mM; leupeptin, 200 microM; pepstatin A, 100 microM; phenylmethanesulfonyl fluoride, 100 microM), neomycin (200 microM), washing with EDTA (5 mM) or by both incubating and washing with delipidized serum albumin (1 mg/ml). During preincubation under optimal Mg2+ and vanadate conditions, the replacement of K+ by Na+ or Li+ was without effect. Co2+ or Zn2+ (10 mM) could not substitute for Mg2+, whereas Mn2+ almost replaced it at equimolar amounts. By contrast, addition of ATPMg (2 mM) decreased the activation by about one-half. Like calmodulin, pretreatment with Mg2+ plus vanadate also increased the affinity for ATP and elicited appearance of a second (low) affinity site (apparent Km = 120 microM). The fluorescence depolarization of 1,6-diphenyl- and 1-(4-trimethylammonium phenyl)-6-phenyl 1,3,5-hexatriene incorporated into membrane fragments was not affected after preincubating with Mg2+, vanadate or Mg2+ plus vanadate. The results show that Mg2+ and vanadate are acting neither via proteolysis or fatty acid production nor by facilitating phospholipid metabolism or altering membrane fluidity. They may be enhancing the Ca(2+)-ATPase activity by stabilizing the E1 conformer or promoting an enzyme conformation which facilitates the E2-E1 transition.