Calcium uptake in brain synaptosomes from rats exposed to daily toluene for up to 80 weeks

Rats were exposed to toluene, 500 p.p.m., for 12 hrs/day for up to 80 weeks. The brains were removed and the synaptosomes were prepared. Potassium-stimulated and unstimulated synaptosomes were incubated with 45Ca2+ for 1/2, 2, 4, 8, and 16 min. Toluene exposure for 4 and 12 weeks caused a significant, approximately 20%, increase in 45Ca2+ uptake into unstimulated synaptosomes. The effect was of moderate quantity and transient, since it was not significant after 30 and 80 weeks of exposure. It seems doubtful whether the demonstrated change in calcium uptake should have any relevance in connection with the "organic solvent neurotoxicity syndrome".

Structure-function relationships in EF-hand Ca2+-binding proteins. Protein engineering and biophysical studies of calbindin D9k

Genes encoding the minor A component of bovine calbindins D9k--the smallest protein known with a pair of EF-hand calcium-binding sites--with amino acid substitutions and/or deletions have been synthesized and expressed in Escherichia coli and characterized with different biophysical techniques. The mutations are confined to the N-terminal Ca2+-binding site and constitute Pro-20----Gly (M1), Pro-20----Gly and Asn-21 deleted (M2), Pro-20 deleted (M3), and Tyr-13----Phe (M4). 1H, 43Ca, and 113Cd NMR studies show that the structural changes induced are primarily localized in the modified region, with hardly any effects on the C-terminal Ca2+-binding site. The Ca2+ exchange rate for the N-terminal site changes from 3 s-1 in the wild-type protein (M0) and M4 to 5000 s-1 in M2 and M3, whereas there is no detectable variation in the Ca2+ exchange from the C-terminal site. The macroscopic Ca2+-binding constants have been obtained from equilibration in the presence of the fluorescent chelator 2-[[2-[bis(carboxymethyl)-amino]- 5-methylphenoxy]methyl]-6-methoxy-8-[bis(carboxymethyl)amino]quinoline or by using a Ca2+-selective electrode. The Ca2+ affinity of M4 was similar to that of M0, whereas the largest differences were found for the second stoichiometric step in M2 and M3. Microcalorimetric data show that the enthalpy of Ca2+ binding is negative (-8 to -13 kJ.mol-1) for all sites except the N-terminal site in M2 and M3 (+5 kJ.mol-1). The binding entropy is strongly positive in all cases. Cooperative Ca2+ binding in M0 and M4 was established through the values of the macroscopic Ca2+-binding constants. Through the observed changes in the 1H NMR spectra during Ca2+ titrations we could obtain ratios between site binding constants in M0 and M4. These ratios in combination with the macroscopic binding constants yielded the interaction free energy between the sites delta delta G as -5.1 +/- 0.4 kJ.mol-1 (M0) and less than -3.9 kJ.mol-1 (M4). There is evidence (from 113Cd NMR) for site-site interactions also in M1, M2, and M3, but the magnitude of delta delta G could not be determined because of sequential Ca2+ binding.

Reduced Ca2+ flux in synaptosomes from cats with GM1 gangliosidosis

Ca2+ transport was studied in synaptosomes prepared from normal cats and cats with GM1 gangliosidosis. The influx of Ca2+ was found to be a biphasic process in synaptosomes from both GM1 mutant and normal cats. Both the fast and slow phases of voltage-dependent Ca2+ uptake were significantly reduced in cats with the lysosomal storage disease, however the inhibitory mechanisms differed. The fast phase of Ca2+ uptake was inhibited uncompetitively, whereas the slow phase was inhibited competitively. In addition, Na+-dependent Ca2+ efflux was reduced significantly in cats with GM1 gangliosidosis. Since it is well established that maintenance of Ca2+ homeostasis is essential for normal neuronal function, a ganglioside-induced disruption of Ca2+ transport across synaptic membranes may be responsible, in part, for the neuronal dysfunction characteristic of GM1 gangliosidosis.

Paradoxical augmentation of (-)Bay K 8644-induced calcium influx by nitrendipine

(-)Bay K 8644 produced a concentration-dependent contraction of porcine coronary artery rings with the maximal contraction at 10(-6) M. Pretreatment of the rings with 10(-6) M nitrendipine inhibited (-)Bay K 8644-induced contraction, while pretreatment with 10(-8) M nitrendipine potentiated the contraction elicited by (-)Bay K 8644. (-)Bay K 8644 (10(-6) M) significantly stimulated Ca2+ influx. Although 10(-8) M nitrendipine never stimulated Ca2+ influx, Ca2+ influx induced by (-)Bay K 8644 was significantly potentiated by pretreatment with 10(-8) M nitrendipine. Pretreatment with 10(-6) M nitrendipine significantly decreased Ca2+ influx in tissues treated with (-)Bay K 8644. Our results suggest that the increased Ca2+ influx might be involved in the mechanisms by which (-)Bay K 8644-induced contraction was potentiated by pretreatment with nitrendipine.

Recovery from calcium-induced damage in a neuroblastoma cell line

Calcium may act as a second messenger in normal cellular signal transduction systems. However, an excessive influx of calcium into the cytoplasm is well known to be a final common pathway causing cell death under various pathological conditions. The purpose of this study was to investigate the effect of a transient treatment with the calcium ionophore A23187 on the recovery process of cell viability, energy metabolism, amino acid incorporation and calcium uptake in a neuroblastoma cell line. When neuroblastoma cells were treated with 20 microM of the calcium ionophore A23187 in combination with extracellular calcium, rapid energy failure and marked inhibition of amino acid incorporation by the cells occurred together with a massive influx of calcium, and finally resulted in cell death. Recovery from this calcium-induced damage with regards to energy metabolism and prognosis of cell viability was better after a 10-min treatment than after a 30-min treatment with A23187. After a 10-min treatment, the viability was higher in calcium-free medium than in calcium-containing medium in contrast with the cases after treatment for 30 min. The above difference in viability after treatment for 10 min had a very significant correlation with the degree of exclusion of excessive calcium and the recovery of CTP, indicating that the recovery of CTP and the rate of calcium exclusion may be final markers of the recovery of cells from calcium-induced damage rather than the recovery of ATP or amino acid incorporation. Amino acid incorporation was restricted to a level lower than that of the control long after the recovery of GTP and the GTP/GDP ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Divalent cation binding to the high- and low-affinity sites on G-actin

Metal binding to skeletal muscle G-actin has been assessed by equilibrium dialysis using 45Ca2+ and by kinetic measurements of the increase in the fluorescence of N-acetyl-N'-(5-sulfo-1-naphthyl)-ethylenediamine-labeled actin. Two classes of cation binding sites were found on G-actin which could be separated on the basis of their Ca2+ affinity: a single high-affinity site with a Kd considerably less than 1 microM and three identical moderate-affinity binding sites with a Kd of 18 microM. The data for the Mg2+-induced fluorescence enhancement of actin labeled with N-acetyl-N'-(5-sulfo-1-naphthyl)ethylenediamine support a previously suggested mechanism [Frieden, C. (1982) J. Biol. Chem. 257, 2882-2886] in which Ca2+ is replaced by Mg2+ at the moderate affinity site(s), followed by a slow actin isomerization. This isomerization occurs independently of Ca2+ release from the high-affinity site. The fluorescence data do not support a mechanism in which this isomerization is directly related to Ca2+ release from the high-affinity site. Fluorescence changes of labeled actin associated with adding metal chelators are complex and do not reflect the same change induced by Mg2+ addition. Fluorescence changes in the labeled actin have also been observed for the addition of Cd2+ or Mn2+ instead of Mg2+. It is proposed actin may undergo a host of subtle conformational changes dependent on the divalent cation bound. We have also developed a method by which progress curves of a given reaction can be analyzed by nonlinear regression fitting of kinetic simulations to experimental reaction time courses.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport and control of Ca2+ by pigeon erythrocytes. III. A 'paradoxical' expulsion of Ca2+ induced by a low dose of A23187 at 0 degrees C

Pigeon erythrocytes expelled preloaded 45Ca2+ in response to a low dose of A23187 at 0 degrees C. We call this phenomenon 'paradoxical' expulsion. Within the first minute, 1.85 +/- 0.38 mumol/l cell water was expelled; after that the internal 45Ca2+ began to rise. The rises in Ca2+ uptake with and without A23187 addition were essentially paralleled. No premonitory rise of 45Ca2+ upon the addition of A23187 was observed. Expulsion of 45Ca2+ in response to A23187 was probably by the action of the Ca2+ pump and not by Na+-Ca2+ exchange since vanadate inhibited, but K+ replacement of Na+ in the medium had no effect. Lysophosphatidylcholine (lysoPC) caused an abrupt increase in 45Ca2+ influx by cells at 0 degrees C and was dose dependent. However, a very low dose of lysoPC induced expulsion of preloaded 45Ca2+ similar to that by A23187, the response was fast and transitory, without any premonitory rise in 45Ca2+ uptake. The results lend support to the suggestion that the signal to which cells respond may be a sudden change in Ca2+ influx per se rather than a change in internal Ca2+ concentration. These features of 'paradoxical' 45Ca2+ expulsion induced by A23187 and lysoPC are not expected from mass-action equilibria but, instead, agree with the characteristics of an energy-dissipating control mechanism.

Lack of effects of calcium X calmodulin-dependent phosphorylation on Ca2+ release from cardiac sarcoplasmic reticulum

Canine cardiac sarcoplasmic reticulum is phosphorylated by an endogenous calcium X calmodulin-dependent protein kinase and phosphorylation occurs mainly on a 27 kDa proteolipid, called phospholamban. To determine whether this phosphorylation has any effect on Ca2+ release, sarcoplasmic reticulum vesicles were phosphorylated by the calcium X calmodulin-dependent protein kinase, while non-phosphorylated vesicles were preincubated under identical conditions but in the absence of ATP to avoid phosphorylation. Both non-phosphorylated and phosphorylated vesicles were centrifuged to remove calmodulin, and subsequently used for Ca2+ release studies. Calcium loading was carried out either by the active calcium pump or by incubation with high (5 mM) calcium for longer periods. Phosphorylation of sarcoplasmic reticulum by calcium X calmodulin-dependent protein kinase had no appreciable effect on the initial rates of Ca2+ released from cardiac sarcoplasmic reticulum vesicles loaded under passive conditions and on the apparent 45Ca2+-40Ca2+ exchange from cardiac sarcoplasmic reticulum vesicles loaded under active conditions. Thus, it appears that calcium X calmodulin-dependent protein kinase mediated phosphorylation of cardiac sarcoplasmic reticulum is not involved in the regulation of Ca2+ release and 45Ca2+-40Ca2+ exchange.

Alaproclate inhibits potassium currents and thereby enhances muscarinic stimulation in N1E-115 neuroblastoma cells

Effects of alaproclate, an inhibitor of the uptake of serotonin, on muscarinic cholinergic responses in N1E-115 neuroblastoma cells were studied using intracellular recording techniques. Application of carbachol activates an inward calcium channel, through an action on muscarinic receptors. The influx of calcium activates potassium channels. Alaproclate was found to block these potassium channels and thereby to prolong the muscarinic cellular response to carbachol. It is suggested that this is one mechanism by which alaproclate potentiates cellular responses to muscarinic cholinergic agonists.

Insulin enhances development of functional voltage-dependent Ca2+ channels in aneurally cultured human muscle

Voltage-dependent Ca2+ channels were studied by the binding of the potent Ca2+ channel antagonist PN200-110 and by the K+-induced 45Ca2+ uptake in human muscle cultured aneurally in the presence of insulin, fibroblast growth factor, and epidermal growth factor, added in combination or individually. Compared to the muscle grown in medium without growth factors, 14-15 days of treatment with insulin (10 micrograms/ml) alone or in combination with two other growth factors caused a 3.4- and 3.8-fold increase per culture dish in the number of PN200-110 binding sites, respectively. There was no change in the affinity of the ligand-receptor complex. Under the same conditions, there was also fourfold increase of the K+-induced 45Ca2+ uptake in cultured human muscle. Neither fibroblast growth factor nor epidermal growth factor alone influenced PN200-110 binding sites. Our study demonstrates that insulin enhances the development of functional voltage-dependent Ca2+ channels in cultured human muscle.

The role of a Ca2+/calmodulin dependent plasma membrane Ca2+ channel during concanavalin A activation of MC9 mast cells

The effects of Con A on free cytoplasmic calcium concentrations in the cloned murine mast cell, MC9, have been measured using the fluorescent calcium indicator quin 2. Con A causes a rapid, small yet sustained rise in free cytosolic calcium (up to 245 nM) followed closely by increased 45calcium uptake and more slowly by histamine release. The increases in 45calcium uptake and histamine release require extracellular calcium. However, the Ca2+ influx blockers, nifedipine and verapamil inhibit these responses only at concentrations significantly higher than those used in smooth muscle to oppose potential-dependent events, and diltiazem is inactive. These observations suggest that, in these mast cells, other types of channels control Ca2+ entry. In contrast, the intracellular Ca2+ blocker, TMB-8, inhibits both the Con A-induced histamine release and the Ca2+ changes. The calmodulin antagonists calmidazolium, trifluoperazine and W-7 are also highly effective inhibitors of both the Ca2+ changes and histamine release in direct proportion to their potency against calmodulin-dependent phosphodiesterase, implicating calmodulin in the regulation of stimulus-secretion in MC9 cells. These data imply that histamine release follows increases in intracellular Ca2+ concentration. Free intracellular Ca2+ results from rapid release from internal stores and is followed by a slower but more sustained influx of extracellular Ca2+.

Periodic courses of human 1-34 parathyroid peptide alternating with calcitriol paradoxically reduce bone remodelling in spinal osteoporosis

In an attempt to achieve an anabolic response in both axial and peripheral bone, we treated twelve patients with osteoporosis using human 1-34 parathyroid peptide given discontinuously. The peptide was given as seven daily subcutaneous injections followed by 21 days' treatment with 0.25 mg calcitriol orally. This regime was repeated cyclically for at least sixteen cycles, of which the first four were at a lower dose of hPTH 1-34 than used subsequently. The results of treatment were monitored by kinetic, densitometric, histomorphometric and biochemical studies performed before and during treatment. Two patients developed hPTH 1-34 binding in their plasma during treatment: this was presumed to be due to the development of antibodies. The remainder, instead of increasing their indices of bone turnover as judged by iliac bone histomorphometry, were found to have consistent reductions in trabecular resorption surfaces. The other indices of bone formation and resorption measured showed no change or comparable reductions. The small increases seen in total body calcium were consistent with 'in-filling' of deleted basic multicellular units (BMUs). Because there is no evidence that calcitriol alone causes comparable reductions in activation of bone remodelling in osteoporosis, interruption of treatment with hPTH 1-34 after 7 days may have led to a failure of the activation mechanism to proceed to the resorption stage, with a consequent overall reduction in remodelling activity. This type of treatment regime, with its calcitonin-like effect, might be effective in reducing net bone loss due to imbalance between bone formation and resorption at the BMU level, particularly in patients with increased numbers of BMUs ('high turnover' osteoporosis).(ABSTRACT TRUNCATED AT 250 WORDS)

Acceleration of cartilage and bone differentiation on collagenous substrata

Chondroprogenitor cells of newborn murine mandibular condyles were cultured on top of collagen sponges for up to 18 days. After 24 h in culture, new chondroblasts developed which subsequently matured showing signs of hypertrophy, while the extracellular matrix revealed positive reactivity for type II collagen, cartilage proteoglycans and mineralization. Light and electron microscopy examinations showed signs of new osteoid formation, a feature that was preceded by positive immunohistochemical reaction for type I collagen, fibronectin and bone specific sialoprotein. A close temporal and spatial association was noted between the development of mature, mineralized cartilage and new osteoid. The differentiation of new cartilage and bone cells was linked to an increased activity of DNA synthesis and cellular proliferation. The de novo bone formation was accompanied by increasing rates of alkaline phosphatase activity and uptake of [45Ca] features that were found to be tightly correlated to each other. The collagen substrata appeared also to facilitate the migration of cells, their replication and their subsequent differentiation to their respective cellular lineage. Hence, collagen sponges in vitro appear to serve as a promising substrata for culture systems involved with the growth and differentiation of mineralizing tissues such as cartilage and bone.

Cation transport by pancreatic beta-cells: effect of 4-aminopyridine on 86Rb+ and 45Ca2+ fluxes

The effects of 4-aminopyridine (4-AP) on insulin release, glucose oxidation and 86Rb+ and 45Ca2+ fluxes of rat isolated islets were studied. 4-AP (0.1 and 1.0 mM) did not alter the 86Rb+ fractional efflux. However, 10 mM 4-AP significantly increased the 86Rb+ fractional efflux. 10 mM 4-AP also reduced the insulin release from islets incubated over 90 min in the presence of both 6 and 16.7 mM glucose and from perifused islet in the presence of 16.7 mM glucose. 4-AP (10 mM) only transiently increased the insulin release and the 45Ca2+ fractional efflux in the presence of 6 mM glucose. The 45Ca2+ fractional efflux was not changed when the islets were perifused at higher glucose concentration. At zero, 6 or 16.7 mM glucose, 4-AP (10 mM) significantly increased the 45Ca2+ net uptake by islets incubated for 90 min. 10 mM 4-AP significantly reduced the glucose oxidation of islets incubated for 120 min in the presence of 16.7 mM glucose. The effects of 10 mM 4-AP on the dynamics of insulin release and 86Rb+ fractional efflux were poorly reversible. In conclusion, 4-AP, at concentrations that did not alter the glucose metabolism, (0.1 and 1 mM), failed to affect the K+ permeability in beta-cells as judged by the measurements of 86Rb+ fractional efflux. At higher concentrations (10 mM) 4-AP increased 86Rb+ efflux, decreased glucose metabolism and reduced insulin release.

[45Ca2+ and 3H-GABA transport in nerve endings separated from the cerebral cortex of rats with hypoparathyroidism]

Ca2+ blood serum level was reduced by 34.5% in rats with hypoparathyroidism (HPT) on the 7th-12th day after the damage of parathyroid glands. Synaptosomes isolated from the brain cortex of rats during this period accumulated in a normal medium more 45Ca2+ than synaptosomes from healthy animals. In potassium depolarization, control and experimental synaptosomes accumulated more 45Ca2+, however in HPT the increment in 45Ca2+ uptake in high potassium medium was less temperature-dependent. In normal medium 3H-GABA uptake and release by synaptosomes from the brain of rats with HPT slightly differed from those in the control. On the contrary, 3H-GABA release induced by synaptosome depolarization was depressed in HPT. It is suggested that nerve terminal excretory function disturbances contribute to increased excitability of the central nervous system in hypoparathyroidism.

Bone matrix and marrow versus cancellous bone in rabbit radial defects

Implants of demineralized bone matrix induce new bone formation. In order to estimate the possible clinical usefulness of this phenomenon, autologous cancellous bone grafts were compared with composite grafts of bone matrix and marrow. Cancellous bone from the tuber ischii of the rabbit was transplanted to a preformed radial defect in the same animal. On the opposite side, a similar defect was filled with a mixture of either allogenous or autogenous bone-matrix particles and autogenous bone marrow. After 25 days, calcium 45 was injected intravenously. Three days later the animals were killed. Standardized segments of the rabbit's forearms, containing the middle of the defect, were cut out, ashed, and analyzed for 45Ca activity. No side difference in 45Ca deposition was found. The callus ash weight of the allogenous matrix-transplanted side was approximately 60% of that of the cancellous bone side. This side difference of ash weights corresponds to the estimated initial mineral content of the cancellous graft. Nontransplanted defects had very low ash weight and 45Ca activity. Thus, in the rabbit, composite grafts of bone matrix and marrow produce a bone yield comparable to that of cancellous bone.

External ATP mimics carbachol in initiating calcium mobilization from pancreatic beta-cells conditioned by previous exposure to glucose

1 Exposure to ATP (2-200 microM) resulted in a prominent peak of 45Ca efflux, when beta-cell-rich pancreatic islets from ob/ob-mice were perifused with a Ca2+-deficient medium. ADP and the stable alpha/beta-methylene analogues of ATP and ADP also had stimulatory effects. 2 The nucleotide initiation of 45Ca efflux mimicked that obtained with carbachol both in requiring previous exposure to glucose and in being more pronounced after replacing extracellular Na+ by K+. 3 It was possible to induce repeated peaks of stimulated 45Ca efflux, when the exposure to ATP was interrupted with intervals of perifusion with glucose-containing media. 4 The observations are consistent with the existence of P2-purinoceptors in islets, suggesting that these receptors mediate a similar mobilization of calcium as noted when activating polyphosphoinositide breakdown with carbachol. In view of the high contents of ATP and ADP in the beta-cell secretory granules, activation of P2-purinoceptors should be considered as a possible mechanism for amplification of the initial insulin secretory response.

Resolution in EM autoradiography V: 45Ca (and 33P)

We devised a specimen to test EM autoradiographic resolution for calcium-45 (and phosphorous-33). A dry emulsion film was used for soluble compounds. We obtained a resolution (HD) value of 2300 +/- 500 A. This value is no larger than that previously obtained for Carbon -14, whose emission is about 1.6-fold lower. This result is as expected on theoretical grounds.

Effects of 1,1,1-trichloroethane on synaptosomal calcium accumulation in mouse brain

Addition of 1,1,1-trichloroethane (TCE), in vitro to synaptosomes isolated from the mouse cerebellum and cerebral cortex inhibited the slow phase of K+-stimulated 45Ca2+ influx and the net 45Ca2+ influx (delta k). In the brain stem, however, TCE increased the fast and slow phases of calcium uptake under depolarizing conditions and also delta k. The non-depolarized calcium influx was not altered by TCE added in vitro. Two hours after injection of TCE (2.4 g/kg) the calcium accumulation in the presence of high K+ was lowered in the cerebellar synaptosomes, while it was increased in brain stem synaptosomes. TCE administered in vivo did not alter the calcium influx into cerebrocortical synaptosomes nor did it affect the non-depolarization-induced 45Ca2+ influx. Thus, these data indicate that TCE may influence voltage-dependent calcium channels in mouse brain synaptosomes.

Kinetic and thermodynamic control of ATP synthesis by sarcoplasmic reticulum adenosinetriphosphatase

Several experimental parameters, critical to the analysis of ATP synthesis by sarcoplasmic reticulum ATPase, were determined experimentally. 1) The phosphorylated enzyme intermediate obtained with acetylphosphate in the presence of a Ca2+ gradient was shown to be entirely ADP sensitive but quite stable in the absence of added ADP. On the contrary, the phosphoenzyme obtained with ATP is unstable due to the ADP formed during the phosphoryl transfer reaction. For this reason, addition of ADP to [32P]phosphoenzyme obtained with [32P]acetylphosphate provides the simplest conditions for kinetic studies on [gamma-32P]ATP synthesis. 2) The dissociation rate constant of newly synthesized ATP (in the reverse direction of the ATPase cycle) was measured experimentally and found to be 16 s-1. This value agrees well with the dissociation rate constant determined for adenyl-5'-yl imidodiphosphate bound to this enzyme. 3) ATP synthesis observed in the absence of a Ca2+ gradient was shown to be a kinetic overshoot due to ligand-induced perturbation of a limited number of partial reactions and occurring before equilibration of the entire system. Most of the ATP formed under these conditions was subsequently hydrolyzed as the overall equilibrium was reached. 4) Based on these and other (previously characterized) parameters, satisfactory simulations of single and multiple cycle ATP synthesis, in the presence and in the absence of a Ca2+ gradient, were obtained.

Modulation of calcium uptake and D-aspartate release by GABAB receptors in cultured cerebellar granule cells

(-)Baclofen, a GABAB receptor agonist, and GABA attenuated by 60% the high K+-evoked 45Ca2+ uptake into cultured cerebellar granule cells with an EC50 of 110 +/- 18 nM and 2.4 +/- 0.2 microM, respectively. The attenuation by baclofen of 45Ca2+ uptake was stereospecific and the effect of GABA was unaffected by bicuculline. Moreover, muscimol, a GABAA receptor agonist did not affect the K+-evoked 45Ca2+ uptake. (-)Baclofen and GABA also decreased the K+-evoked and calcium-dependent release of preloaded [3H]D-aspartate from granule cells; however, their potency and efficacy appeared to be less than those for inhibiting the 45Ca2+ uptake. (+)Baclofen and muscimol failed to change this K+-evoked release. The release of [3H]D-aspartate induced by the calcium ionophore A23187 was unaffected by (-)-baclofen. The K+-evoked release of [3H]D-aspartate was effectively inhibited by nimodipine, a voltage sensitive calcium channel blocker. The results suggest that GABAB receptor in cultured cerebellar granule cells plays a crucial role in modulating the uptake of calcium and release of the excitatory transmitter. Moreover, these two effects mediated by GABAB receptor activation may be casually related.

Gingerol, a novel cardiotonic agent, activates the Ca2+-pumping ATPase in skeletal and cardiac sarcoplasmic reticulum

Gingerol, isolated as a potent cardiotonic agent from the rhizome of ginger, stimulated the Ca2+-pumping activity of fragmented sarcoplasmic reticulum (SR) prepared from rabbit skeletal and dog cardiac muscles. The extravesicular Ca2+ concentrations of the heavy fraction of the fragmented SR (HSR) were measured directly with a Ca2+ electrode to examine the effect of gingerol on the SR. Gingerol (3-30 microM) accelerated the Ca2+-pumping rate of skeletal and cardiac SR in a concentration-dependent manner. The rate of 45Ca2+ uptake of HSR was also increased markedly by 30 microM gingerol without affecting the 45Ca2+ efflux from HSR. Furthermore, gingerol activated Ca2+-ATPase activities of skeletal and cardiac SR (EC50, 4 microM). The activation of SR Ca2+-ATPase activity by gingerol (30 microM) was completely reversed by 100-fold dilution with the fresh saline solution. Kinetic analysis of activating effects of gingerol suggests that the activation of SR Ca2+-ATPase is uncompetitive and competitive with respect to Mg . ATP at concentrations of 0.2-0.5 mM and above 1 mM, respectively. Kinetic analysis also suggests that the activation by gingerol is mixed-type with respect to free Ca2+ and this enzyme is activated probably due to the acceleration of enzyme-substrate complex breakdown. Gingerol had no significant effect on sarcolemmal Ca2+-ATPase, myosin Ca2+-ATPase, actin-activated myosin ATPase and cAMP-phosphodiesterase activities, indicating that the effect of gingerol is rather specific to SR Ca2+-ATPase activity. Gingerol may provide a valuable chemical tool for studies aimed at clarifying the regulatory mechanisms of SR Ca2+-pumping systems and the causal relationship between the Ca2+-pumping activity of SR and muscle contractility.

Red blood cells Ca2+ pump is not altered in essential hypertension of humans and Kyoto rats

The kinetic parameters of the Ca2+ pump were assessed in red blood cells of essential hypertensive subjects as compared to their respective controls. Uphill Ca2+ efflux was investigated in Ca2+ -saturated intact red blood cells using a new method recently developed for human red cells (Dagher,G. and Lew, V. J. Physiol. (London), in the press). 45Ca-equilibrated cells were obtained using ionophore A23187 and Ca2+ efflux was assessed after addition of excess CoCl2 which totally inhibits Ca2+ influx and thus exposes uphill Ca2+ extrusion by the pump. The results comprise methodological aspects of the use of this technique in rat red blood cells. The determination of the maximal velocity and the Ca2+ concentration for half-maximal stimulation (KCa 0.5) did not reveal any alteration in essential hypertensives and spontaneously hypertensive rats as compared to their controls.

Diminution of contractile response of the aorta from endotoxin-injected rats

The contractility of a helical strip of the thoracic aorta was studied in rats injected intraperitoneally with endotoxin. The contractile response to any of the agonistic agents, KCl, norepinephrine or 5-hydroxytryptamine was time dependently diminished in the endotoxin-injected rats compared to the controls. This diminution preceded the depression of blood pressure. When the external calcium concentration was increased from 2.5 to 7.5 mM after the KCl (80 mM)-induced contractile response reached a plateau, the diminished contractile response was reversed in the endotoxin-injected group. The strips from the endotoxin-injected rats showed a higher 45CaCl2 uptake into the vascular tissue with the KCl-stimulated contraction. These findings suggest that the blood pressure depression during endotoxic shock may be attributed partially to the diminished contractility of the blood vessels and that this diminution is induced by a disorder of calcium utilization within vascular smooth muscle during vascular contraction.