The inhibition of the sarcoplasmic calcium pump by prenylamine, reserpine, chlorpromazine and imipramine

Hepatoprotective Effect of Ethanolic Extract of Garlic Against Reserpine Induced Toxicity in Wistar Rats

Reserpine, a bioactive compound isolated from the roots of Rauwolfia serpentine, is known to deplete dopamine, a neurotransmitter. The clinical application of reserpine has been associated to manage hypertension, insanity, insomnia and schizophrenia. However, the usage of reserpine as a drug is restricted because of its ability of inducing excess free radicals production and oxidative stress resulting into damage to liver and other organs. Here, we have explored the antioxidative potential of extract of garlic prepared using ethanol (EEG) against reserpine-induced hepatic damage in the albino Wister rats.The animals were divided into four different groups containing 6 animals in each: (1) control + placebo, (2) control + EEG, (3) reserpine and (4) reserpine with EEG. The reserpine treatment resulted into sharp increase in the level of MDA and significant reduction in the activitiesof key antioxidative enzymes (SOD, GST, and CAT) in the rat liver. It also caused sharp perturbations in the levels of certain hepatic transaminases (ALT, AST) and glycolytic LDH. The histopathological results revealed hepatic necrosis, which could have occurred due to reserpine induced lipid peroxidation as well as reduction in the levels of antioxidant species.The administration of EEG, however, significantly ameliorated reserpine induced hepatotoxicity. These results reflected the ameliorative property of EEG, which was probably mediated via its antioxidant function as it contains several bioactive molecules with free radical quenching potential.This study suggestedthe prospective application of EEG as a supplement to combat the side effects of reserpine.

Effects of chlorpromazine on excitation-contraction coupling events in fast-twitch skeletal muscle fibres of the rat

1. Single mechanically skinned fibres from the rat extensor digitorum longus muscle, which allow access to intracellular compartments, were used to examine the effects of 0.5-100 microM chlorpromazine hydrochloride (CPZ) on the major steps of the excitation-contraction (E-C) coupling to elucidate the involvement of skeletal muscle in the neuroleptic malignant syndrome (NMS). 2. At 1 microM, CPZ caused a 20-30% increase in the force response induced by t-system depolarisation and a marked increase in the rate of caffeine-induced SR Ca(2+) release. At [CPZ]> or =2.5 microM, there was an initial increase followed by a marked decrease of the t-system depolarisation-induced force responses, while the potentiating effect on the caffeine-induced SR Ca(2+) release remained. These effects were reversible. 3. CPZ had no effect on the maximum Ca(2+)-activated force, but caused reversible, concentration-dependent increases in the Ca(2+) sensitivity of the contractile apparatus at [CPZ] > or =10 microM, with a 50% predicted shift of 0.11 pCa (-log [Ca(2+)]) units at 82.3 microM CPZ. 4. CPZ did not alter the rate of SR-Ca(2+) loading at 1 and 10 microM, but reversibly reduced it by approximately 40% at 100 microM by reducing the SR Ca(2+) pump. Nevertheless, the SR Ca(2+) content was greater when fibres became unresponsive to t-system-induced depolarisation in the presence than in the absence of 100 microM CPZ. 5. The results show that CPZ has concentration-dependent stimulatory and inhibitory effects on various steps of the E-C coupling, which can explain the involvement of skeletal muscle in NMS and reconcile previous divergent data on CPZ effects on muscle.

Effect of antidepressants on ATP-dependent calcium uptake by neuronal endoplasmic reticulum

This study investigated the effect of tricyclic and atypical antidepressants on adenosine triphosphate (ATP) dependent calcium uptake by the endoplasmic reticulum of lysed synaptosomes from rat brain cortex. Tricyclic antidepressants (imipramine, desipramine, clomipramine, amitriptyline) exhibited no effect in the lower range (0.06 to 2 µM) of drug concentrations, and a concentration-dependent inhibition of calcium uptake in the upper range (6 to 200 µM). A concentration-dependent inhibition was observed for atypical antidepressants (mianserin, desmethylmianserin, venlafaxine, desmethylvenlafaxine, fluoxetine) in both the lower and the upper range of drug concentrations. Since no stimulation of calcium uptake was observed in either concentration range, it appears that the tricyclic and atypical antidepressants tested are not capable of normalizing, through their effect on the endoplasmic reticulum, an overactive calcium signal, which is possibly implicated in the etiology of affective disorders. Also, although only marginal inhibition of calcium uptake is expected at brain concentrations of tricyclics and mianserin–desmethylmianserin that are likely to be encountered during clinical use, a more substantial inhibition could occur with fluoxetine.Key words: adenosine triphosphate-dependent calcium uptake, neuronal endoplasmic reticulum, lysed brain synaptosomes, tricyclic antidepressants, atypical antidepressants.

Sarcoplasmic ionic calcium concentration in neuroleptic malignant syndrome

The neuroleptic malignant syndrome (NMS) is an uncommon but serious adverse effect of antipsychotic medication. Similarities in the clinical picture, and muscle alterations, between NMS and susceptibility to malignant hyperthermia (MH) suggest common mechanisms underlying both disorders. Sarcoplasmic ionic calcium concentration ([Ca2+]i) was measured by means of Ca2+ selective microelectrodes in intact intercostal muscle fibers isolated from NMS patients and from subjects with no evidence of neuromuscular disease, who served as controls. The mean resting membrane potential and [Ca2+]i were -84 +/- 0.4 mV and 0.11 +/- 0.01 microM (mean +/- SEM) in the control subjects, while they were -84 +/- 0.6 mV and 0.51 +/- 0.02 microM in NMS muscle fibers. Only the difference in [Ca2+]i is significant (P less than 0.001). The incubation of control and NMS muscle bundles in dantrolene (10(-6) M) induced a reduction of [Ca2+]i to 0.06 +/- 0.01 microM and 0.20 +/- 0.04 microM respectively. These results show an alteration in sarcoplasmic ionic [Ca2+] in NMS muscle fibers, suggesting that a dysfunction in skeletal muscle plays some role in the pathogenesis of NMS.

Pharmacology of calcium release from sarcoplasmic reticulum

Calcium release from sarcoplasmic reticulum (SR) has been elicited in response to additions of many different agents. Activators of Ca2+ release are here tentatively classified as activators of a Ca2+-induced Ca2+ release channel preferentially localized in SR terminal or as likely activators of other Ca2+ efflux pathways. Some of these pathways may be associated with several different mechanisms for SR Ca2+ release that have been postulated previously. Studies of various inhibitors of excitation-contraction coupling and of certain forms of SR Ca2+ release are summarized. The sensitivity of isolated SR to certain agents is unusually affected by experimental conditions. These effects can seriously undermine attempts to anticipate effects of the same pharmacological agents in situ. Finally, mention is made of a new preparation ("sarcoballs") designed to make the pharmacological study of SR Ca2+ release more accessible to electrophysiologists, and some concluding speculations on the future of SR pharmacology are offered.

Calmodulin-antagonist drugs and porcine malignant hyperpyrexia

1. Landrace swine were identified as malignant hyperpyrexia susceptible (MHS) or control by the contracture responses of gracilis muscle fibre bundles to 3% halothane, 2 mmol/l caffeine and 80 mmol/l KCl. The effects of calmodulin-antagonist drugs on the contractile behaviour of control and MHS preparations were investigated in vitro. 2. Calmodulin-antagonists at micromolar concentrations induced contracture in both control and MHS muscle. Pretreatment of MHS muscle with calmodulin-antagonist drugs potentiated its response to halothane and caffeine. 3. These results suggest that calmodulin-antagonist drugs cause an increase in myoplasmic Ca2+ concentration in both control and MHS muscle.

Drug-induced calcium release from heavy sarcoplasmic reticulum of skeletal muscle

Calcium release from isolated heavy sarcoplasmic reticulum of rabbit skeletal muscle by several calmodulin antagonistic drugs was measured spectrophotometrically with arsenazo III and compared with the properties of the caffeine-induced calcium release. Trifluoperazine and W7 (about 500 microM) released all actively accumulated calcium (half-maximum release at 129 microM and 98 microM, respectively) in the presence 0.5 mM MgCl2 and 1 mg/ml sarcoplasmic reticulum protein; calmidazolium (100 microM) and compound 48/80 (70 micrograms/ml) released maximally 30-40% calcium, whilst bepridil (100 microM) and felodipin (50 microM) with calmodulin antagonistic strength similar to trifluoperazine (determined by inhibition of the calcium, calmodulin-dependent protein kinase of cardiac sarcoplasmic reticulum) did not cause a detectable calcium release, indicating that this drug-induced calcium release is not due to the calmodulin antagonistic properties of the tested drugs. Calcium release of trifluoperazine, W7 and compound 48/80 and that of caffeine was inhibited by similar concentrations of magnesium (half-inhibition 1.4-4.2 mM compared with 0.97 mM for caffeine) and ruthenium red (half-inhibition for trifluoperazine, W7 and compound 48/80 was 0.22 microM, 0.08 microM and 0.63 micrograms/ml, respectively, compared with 0.13 microM for caffeine), suggesting that this drug-induced calcium release occurs via the calcium-gated calcium channel of sarcoplasmic reticulum stimulated by caffeine or channels with similar properties.

Identification and characterization of a Mg2+-dependent and an independent Ca+2-ATPase in microsomal membranes of rat testis

Rat testicular microsomal membrane fraction contains both Mg+2-dependent and Mg+2-independent Ca+2-ATPase activity. The latter activity is about two times higher than the former. Calcium ion required for maximum activation of Mg+2-independent Ca+2-ATPase in 3.0 mM, whereas for the dependent one it is 2.5 mM. Both the enzymes are resistant to cold shock upto seven days. Histidine and imidazole buffers are found to be the most suitable for dependent and independent enzyme activities, respectively. The pH optima for dependent one is 7.5, whereas for the independent one it is 8.5. Temperature optima for the former is 37 degrees C and for latter one it is 40 degrees C. Among all the nucleotides tested, ATP is found to be the best substrate for both the enzymes. The optimum concentration of ATP for dependent and independent enzyme activities are 3.0 mM and 1.5 mM respectively. Divalent metal ions like Zn+2, Ba+2 and Mn+2 have been found to inhibit Mg+2-dependent Ca+2-ATPase activity whereas Mg+2-independent Ca+2-ATPase activity is inhibited by the divalent ions except zinc which is found to stimulate the enzyme activity. Both the enzymes are inhibited by vanadate, EDTA and EGTA. I50, for vanadate is 0.05 and 0.125 mM for dependent and independent activities, respectively. Sulfhydryl groups modifying agents e.g., NEM, DTNB and chlorpromazine are found to affect the enzyme activities in different ways. Thus NEM and chlorpromazine are found to inhibit and DTNB stimulate the enzyme activities in both the cases.

The effect of reserpine on the pars intermedia of the rat pituitary. An electron-microscopic, fluorescence-histochemical and immunohistochemical study

Reserpine has a stimulatory effect on the pars intermedia of the rat pituitary, probably mediated by its action on regulatory catecholaminergic nerves. The effect of single intraperitoneal injections of 0.1-20 mg/kg b.w. of reserpine was studied in adult male rats. Reserpine at a dose of 2 mg/kg b.w. induced degranulation, orientation of the secretory granules along the cell membrane and loss of formaldehyde-chloral-induced fluorescence, accompanied by an activation of the granular endoplasmic reticulum and the Golgi apparatus. With higher doses progressive degranulation and loss of fluorescence were observed. The effect was, however, heterogeneous, and with all doses cells displaying normal ultrastructure and normal fluorescence were regularly present. To study the release of granular products (containing a different components of the pro-opiomelanocortin chain) from individual cells, formaldehyde-chloral induced fluorescence and alpha-MSH- and beta-endorphin immunoreactivies were demonstrated in consecutive sections from pituitaries of rats given 8 mg/kg body weight of reserpine 24 h before sacrifice. The results indicate coordinated release of these granular products at the cellular level after reserpine treatment.

The effect of phenothiazines on Ca2+ fluxes in skeletal muscle sarcoplasmic reticulum

The effect of phenothiazines (trifluoperazine, chlorpromazine, methochlorpromazine, and imipramine) on Ca2+ fluxes in light and heavy sarcoplasmic reticulum (SR) isolated from rabbit fast-twitch skeletal muscle was investigated. These drugs inhibited Ca2+ loading and (Ca2+,Mg2+)-ATPase activity, but had no effect on unidirectional Ca2+ efflux from vesicles loaded either actively or passively with Ca2+. Chlorpromazine, which is membrane permeable, and its quaternary analog, methochlorpromazine, which is membrane impermeable, gave identical results. It is concluded that (a) the enhancement of net Ca2+ release by phenothiazines is due to inhibition of Ca2+ influx mediated by the Ca2+ pump rather than to the opening of a Ca2+ channel; and (b) phenothiazines act at the outer (myoplasmic) face of the SR membrane.

Comparison of the calmodulin antagonists compound 48/80 and calmidazolium

The two presumed calmodulin antagonists calmidazolium and compound 48/80 were compared for their effects on several calmodulin-dependent and calmodulin-independent enzyme systems. Compound 48/80 and calmidazolium were found to be about equipotent in antagonizing the calmodulin-dependent fraction of brain phosphodiesterase and erythrocyte Ca2+-transporting ATPase. Compound 48/80 combines high potency with high specificity in that: (1) the basal, calmodulin-independent, activity of calmodulin-regulated enzymes was not suppressed; (2) calmodulin-independent enzyme activities, such as Ca2+-transporting ATPases of sarcoplasmic reticulum, Mg2+-dependent ATPases of different tissues and Na+/K+-transporting ATPase of cardiac sarcolemma, were far less altered, or not altered at all, by compound 48/80 as compared with calmidazolium; and (3) antagonism of proteolysis-induced stimulation as opposed to calmodulin-induced activation of erythrocyte Ca2+-transporting ATPase required a 32 times higher concentration of compound 48/80. In all these aspects compound 48/80 was found to be a superior antagonist to calmidazolium since inhibition of calmodulin-independent events by the other agent occurred at considerably lower concentrations. Therefore compound 48/80 is proposed to be a much more specific and useful tool for studying the participation of calmodulin in biological processes than the presently used agents.

The Ca2+ permeability of sarcoplasmic reticulum vesicles. II. Ca2+ efflux in the energized state of the calcium pump

Ca2+ efflux from sarcoplasmic reticulum vesicles was studied by measurements of net Ca2+ uptake, 45Ca2+ flux and hydrolysis of energy-rich phosphate. The maximal Ca2+ uptake capacity (150-200 nmol/mg protein at pH 6.7, 10 mM MgCl2 and mu = 0.26) was independent of the nature and concentration of the energy-donating substrate (ATP or carbamyl phosphate) and of temperature (15-35 degrees C), suggesting coupling between influx and efflux of Ca2+. In the presence of high concentrations of ATP, this efflux of Ca2+ was much higher than the passive Ca2+ permeation, measured after ATP or Ca2+ depletion of the reaction medium. Ca2+ efflux was imperceptible at vesicle filling levels below 35-40 nmol Ca2+/mg protein, and uncorrelated to the inhibition of the Ca2+-ATPase by high intravesicular Ca2+ concentrations. Analysis of the data indicated that Ca2+ efflux under our conditions probably is associated with one of the Ca2+-ATPase partial reactions, occurring after dephosphorylation, rather than with a reversal of the Ca2+ translocation step in the phosphorylated state of the enzyme. Furthermore, passive Ca2+ permeation may be concurrently reduced during the enzymatically active state. It is proposed that both Ca2+ efflux and passive Ca2+ permeation (Ca2+ outflow) proceed via the same channels which are closed (occluded) during part of the Ca2+-ATPase reaction cycle.

The effect of trifluoroperazine on the sarcoplasmic reticulum membrane

The inhibitory effect of trifluoroperazine (25-200 microM) on the sarcoplasmic reticulum calcium pump was studied in sarcoplasmic reticulum vesicles isolated from skeletal muscle. It was found that the lowest effective concentrations of trifluoroperazine (10 microM) displaces the Ca2+ dependence of sarcoplasmic reticulum ATPase to higher Ca2+ concentrations. Higher trifluoroperazine concentrations (100 microM) inhibit the enzyme even at saturating Ca2+. If trifluoroperazine is added to vesicles filled with calcium in the presence of ATP, inhibition of the catalytic cycle is accompanied by rapid release of accumulated calcium. ATPase inhibition and calcium release are produced by identical concentrations of trifluoroperazine and, most likely, by the same enzyme perturbation. These effects are related to partition of trifluoroperazine ino the sarcoplasmic reticulum membrane, and consequent alteration of the enzyme assembly within the membrane structure, and of the bilayer surface properties. The effect of trifluoroperazine was also studied on dissociated ('chemically skinned') cardiac cells undergoing phasic contractile activity which is totally dependent on calcium uptake and release by sarcoplasmic reticulum, and is not influenced by inhibitors of slow calcium channels. It was found that trifluoroperazine interferes with calcium transport by sarcoplasmic reticulum in situ, as well as with the role of sarcoplasmic reticulum in contractile activation.

Induced Ca2+ release in skeletal muscle sarcoplasmic reticulum by sulfhydryl reagents and chlorpromazine

Sarcoplasmic reticulum is a specialized membrane system in muscle involved in the energized uptake, storage, and release of Ca2+. The sulfhydryl content of normal and reconstituted sarcoplasmic reticulum was measured using Ellman reagent. For both preparations, we find 17 and 26 mol sulfhydryls per mole calcium pump protein assayed in the absence and presence of sodium dodecyl sulfate. The release of Ca2+ from sarcoplasmic reticulum, which triggers muscle contraction, likely involves the regulation of a channel. This report deals with an experimental approach to studying the Ca2+ release in isolated sarcoplasmic reticulum. We find that sulfhydryl agents of which water-soluble mercurials were most effective induce Ca2+ release. Chlorpromazine acts synergistically with the sulfhydryl reagents. Ca2+ release under optimal conditions is very rapid compared with calcium leakage from preloaded but untreated sarcoplasmic reticulum. The imposed rapid release of Ca2+ is suggestive of the opening of a channel. Ca2+ release by mercurials is retained in reconstituted sarcoplasmic reticulum membrane vesicles.

Multiple effects of reserpine on chromaffin-granule in membranes

The tranquilizer reserpine has several effects on adrenal medullary chromaffin-granule membrane vesicles (ghosts). At low concentrations (0.20 +/0 0.12 nmol/mg of membrane protein), reserpine inhibits proton-linked epinephrine uptake but does not affect transmembrane pH and electrical potential gradients. Reserpine apparently binds to and blocks the catecholamine translocator. At intermediate concentrations (14.3 +/- 4.8 nmol/mg of membrane protein), reserpine abolishes the ATP-dependent enhancement of 8-anilinonaphthalene-1-sulfonate fluorescence without affecting the ATP-dependent membrane potential. At high concentrations (550 +/- 390 nmol/mg of membrane protein), reserpine stimulates the efflux of epinephrine from preloaded chromaffin-granule ghosts. Because it is highly hydrophobic, reserpine partitions into the membrane and probably exerts a nonspecific detergent-like action. At high concentrations (74 +/- 25 nmol/mg of lipid), reserpine also increases the permeability of phospholipid vesicles to epinephrine. The effectiveness of reserpine in inhibiting epinephrine transport correlates with the reserpine/membrane ratio but not with the molar concentration. This may account for the larger variation in reports of effective reserpine concentrations.

The effect of diazepam on tension and electrolyte distribution in frog muscle

The effect of diazepam on sartorius muscles of the frog was evaluated. Resting tension in sartorius muscle was not affected by diazepam (5 x 10(-5)M) but twitch tension was increased and tetanus tension decreased. The kinetics of 45Ca efflux were altered by diazepam. The calcium content of the intermediate pool was increased by diazepam (5 x 10(-6)M). When the diazepam concentration was increased (5 x 10(-5)M), the time constant of the slow pool decreased and the 45Ca content of the intermediate pool increased further. It is suggested that diazepam interferes with the calcium sequestering system of the sarcoplasmic reticulum (slow pool) and causes an increase of the calcium content of the myofibrillar space (intermediate pool).

Dissociation between Ca2+-ATPase and alkaline phosphatase activities in plasma membranes of rat duodenum

The presence of Ca2+-ATPase activities with high-affinity sites for Ca2+ in brush border as well as basolateral plasma membranes of rat duodenal epithelium has been reported previously (Ghijsen, W.E.J.M. and van Os, C.H. (1979) Nature 279, 802-803). Since both plasma membranes contain alkaline phosphatase (EC 3.1.3.1), which also can be stimulated by Ca2+, the substrate specificity of Ca2+-induced ATP-hydrolysis has been studied to determine whether or not alkaline phosphatase and Ca2+-ATPase are two distinct enzymes. In basolateral fragments, the rate of Ca2+-dependent ATP-hydrolysis was greater than that of ADP, AMP and p-nitrophenylphosphate at Ca2+ concentrations below 25 muM. At 0.2 mM Ca2+ the rates of ATP, ADO, AMO and p-nitrophenylphosphate hydrolysis were not significantly different. In brush border fragments the rates of ATP, ADP and AMP hydrolysis were identical at low Ca2+, but at 0.2 mM Ca2+, Ca2+-induced hydrolysis of ADO and AMO was greater than either ATP or p-nitrophenylphosphate. Alkaline phsophatase in brush border and basolateral membranes was inhibited by 75% after addition of 2.5 mM theophylline. Ca2+-stimulated ATP hydrolysis at 1 muM Ca2+ was not sensitive to theophylline in basolateral fragments while the same activity in brush border fragments was totally inhibited. At 0.2 mM Ca2+, Ca2+-induced ATP hydrolysis in both basolateral and brush border membranes was sensitive to theophylline. Oligomycin and azide had no effect on Ca2+-stimulated ATP hydrolysis, either at low or at high Ca2+ concentrations. Chlorpromazine fully inhibited Ca2+-stimulated ATP hydrolysis in basolateral fragments at 5 muM Ca2+, while it had no effect in brush border fragments. From these results we conclude that, (i) Ca2+-ATPase and alkaline phosphatase are two distinct enzymes, (ii) high-affinity Ca2+-ATPase is exclusively located in basolateral plasma membranes, (iii) alkaline phosphatase activity, present on both sides of duodenal epithelium is stimulated slightly by low Ca2+ concentrations, but this Ca2+-induced activity is inhibited by theophylline and shows no specificity with respect to ATP, ADP or AMP.

Uptake and energy-dependent extrusion of calcium in neural cells in culture

The metabolism of Ca2+ was studied in a neuronal model system, the clonal mouse neuroblastoma x rat glioma hybrid cell line 108CC5. 1. Homogenates of the hybrid cells exhibit a specific activity of Ca2+-ATPase considerably higher than that of homogenates of the parental cells. 2. Uptake and release of 45Ca2+ by the hybrid cells display two and three distinct phases, respectively, and indicate that 40--50% of the cell-associated Ca2+ is located at the cell surface. 3. The influx of 45Ca2+ is insignificantly affected by Mg2+ or Na+, slightly diminished by Ba2+ or Sr2+, strongly inhibited by La3+, Co2+ or prenylamine, and considerably enhanced by high (i.e., depolarizing) concentrations of K+. The efflux of 45Ca2+ is reduced by La3+. 4. The hybrid cells tend to maintain Ca2+ homeostasis with an overall cellular Ca2+ concentration of 0.5--0.7 mM. At 1.8 mM Ca2+ in the medium this implies the necessity of an extrusion pump in the plasma membrane. 5. A reduction in the hybrid cells of the level of ATP is paralleled by a decline in the content of Ca2+. This can only be explained by the existence of energy-dependent intracellular Ca2+ stores that effectively compete for Ca2+ with a Ca2+ pump located in the plasma membrane. The internal stores are not identical with the mitochondria because mitochondrial inhibitors hardly change Ca2+ metabolism. 6. Micromolar concentrations of the ionophore A23187 can switch off the internal Ca2+ stores without affecting considerably the influx of Ca2+ through the plasma membrane. 7. With switched-off Ca2+ stores it is possible to increase the cellular Ca2+ content distinctly and to bring it back again to the control values in an ATP-dependent manner, i.e. to demonstrate the action of a Ca2+-extrusion pump in the plasma membrane. 8. Under some conditions active extrusion of Ca2+ depends not only on ATP but also on the presence of extracellular Na+. 9. Similar results as with hybrid cells are also obtained with rat glioma cells. The methodology of combining energy deprivation with the application of the ionophore A23187 is possibly generally applicable to obtain insight into the Ca2+ metabolism of various cell types.

Studies on the relationship between Ca2+ efflux from mitochondria and the release of amino acid neurotransmitters

It is known that transmitter release depends upon the entry of calcium ions into the synaptic terminal. Mitochondria have been suggested to play a key role on the regulation of intracellular Ca2+ concentration, thereby influencing transmitter liberation and synaptic transmission. Here we report the stimulatory effect of DNP and FCCP, uncouplers of oxidative phosphorylation, and quinidine, known to induce muscle contractures and increase Ca2+ efflux from muscle mitochondria, on both [14C]glutamic acid and [3H]GABA unstimulated release from synaptosomes and loss of 45Ca2+ from preloaded whole brain mitochondria. Results showed that the spontaneous efflux of non-putative neurotransmitters, leucine and alpha-aminoisobutyric acid, was less affected or not stimulated at all, under similar experimental conditions. Data suggest that calcium ions released from mitochondria are able to trigger neurotransmitter release.

Stimulatory and inhibitory effects of dimethylsulfoxide, propranolol and chlorpromazine on the partial reactions of ATPase of sarcoplasmic reticulum

The effects of dimethylsulfoxide, propranolol and chlorpromazine on the partial reactions of the ATPase of sarcoplasmic reticulum were investigated. When analyzed according to a reaction scheme in which the ADP-sensitive (E1P) and ADP-insensitive (E2P) phosphoenzymes occur sequentially and P1 is derived from the latter, dimethylsulfoxide decreased the rate of E2P hydrolysis whereas it stimulated the rate of the E1P to E2P conversion. Propranolol increased the rate of E2P hydrolysis while it decreased the rate of the E1P to E2P conversion. Propranolol exerted an additional effect, presumably inhibition of the phosphoenzyme formation. These effects of dimethylsulfoxide and propranolol can account for both the stimulatory and inhibitory effects of these drugs on the overall rate of ATP hydrolysis observed in the presence and absence of added alkali metal salts. Chlorpromazine accelerated E2P hydrolysis whereas it appeared to inhibit the E1P to E2P conversion. These effects of chlorpromazine appear able to account for its stimulatory and inhibitory effects on the overall rate of ATP hydrolysis in the presence and absence of alkali metal salts. In the presence of chlorpromazine, however, the rate of Pi liberation during the steady state ATP hydrolysis was found to be greater than the hydrolysis rate of E2P. This finding suggests that under these conditions Pi is derived not only from E2P but also from source(s) other than E2P.

The action of chlorpromazine at an isolated cholinergic synapse

The effects of chlorpromazine (CPZ) on cholinergic transmission were studied at the isolated neuromuscular synapse of the frog. It was found that 5 x 10(-6) M CPZ produces the following effects: (1) a reduction in end-plate potential amplitude, mainly through inhibition of transmitter release at presynaptic nerve terminals; (2) a reduction in amplitude of focally recorded end-plate current without detectable change in nerve terminal potential: (3) a decrease in amplitude of miniature end-plate potentials; and (4) an increase in the frequency of spontaneous liberation of transmitter both in normal and calcium-free Ringer's solution. It is concluded that CPZ inhibits cholinergic transmission by a complex action on presynaptic and postsynaptic elements. The relation of these findings to central cholinergic activities of CPZ is discussed.

Diazepam inhibits myoblast fusion and expression of muscle specific protein synthesis

The presence of diazepam in culutres of chicken embryo myoblasts arrests normal muscle cell differentiation. High concentrations of the drug reversibly prevent myoblasts from fusing to form multinucleated myotubes. Lower concentrations of diazepam allow cell fusion to occur, but inhibit the synthesis and accumulation of myosin heavy chain, implying that cell fusion does not obligate myoblasts to synthesize and accumulate large quantities of muscle specific protein. The effect of diazepam on muscle cells in culture is direct and specific.

Interactions between prostaglandins and calcium: the importance of bell-shaped dose-response curves

Biological responses to PGs show two basic forms of dose/response relationship, plateau and bell-types. Although bell-shaped dose/response curves are well documented their possible occurrence is almost always ignored in the design and interpretation of experiments on PGs and related substances. This may lead to serious errors, several types of which are described. The ignoring of a well-documented phenomenon may take place because there is no accepted hypothesis which attempts to explain the bell-type curves. A hypothesis is proposed which accounts for both plateau and bell type responses. It is developed primarily with respect to PG-calcium interactions but may be applicable to some PG-cyclic nucleotide interactions as well. The model leads to precise predictions which can be experimentally tested in many systems.

The sarcoplasmic calcium pump - a most efficient ion translocating system

In contrast to the sodium-potassium transporting plasma membranes, the sarcoplasmic membranes (SR) are highly specialized structures into which only two major intrinsic proteins, a calcium transporting protein and a calcium binding protein are embedded. The calcium transporting protein is a highly asymmetric molecule. It binds two calcium ions with a very high affinity at its external, and two calcium ions with low affinity at the internal section of the molecule. ATP is bound with high afffinity to an external binding site, inducing a conformational change. When the vesicular membranes are exposed to solutions containing Ca++, Mg++ and ATP, ATP is hydrolyzed and simultaneously calcium ions are translocated from the external medium into the vesicular space. When calcium ions are translocated in the opposite direction, ATP is synthesized. The calcium-ATP ratio for ATP cleavage as well as for ATP synthesis is 2. Thus, the SR membranes can transform reversibly chemical into osmotical energy. Inward and outward movements of calcium ions are relatively slow processes connected with the appearance and disappearance of different phosphorylated intermediates. One phosphorylated intermediate is formed by phosphoryltransfer from ATP when calcium ions are present in the medium. In contrast, when calcium ions are absent from the external medium, two different intermediates can be formed by the incorporation of inorganic phosphate. Only when calcium ions present in the internal space of the vesicles are released, the incorporation of inorganic phosphate gives rise to an intermediate who phosphoryl group can be transferred to ADP.

Cardiovascular effects of amitriptyline in anaesthetized dogs

1. The effect of amitriptyline on cardiovascular variables has been studied in anaesthetized dogs. 2. In small doses (0.25 mg/dg) amitryptyline caused small increases in heart rates, contractility, blood pressure, coronary blood flow and aortic flow. 3. Large doses produced initial depressant effects on myocardial reflex rises in these and rate and blood pressure, which were followed by secondary reflex rises in these measurements. 4. The depressant effects were dose-related and were accompanied by marked increases in coronary flow and smaller increases in ortic flow. 5. The secondary reflex rises in cardiac parameters were abolished by propranolol and that of the blood pressure was much reduced.

Ca2+ -uptake into noradrenaline-storing granules of bovine splenic nerves

Noradrenaline-storing granules, a mitochondrial fraction and a microsomal fraction of bovine splenic nerve trunks were prepared by differential centrifugation. These particulate fractions were characterized by their noradrenaline content, succinate dehydrogenase and glucose-6-phosphatase activity. In the presence of ATP-Mg2+ all three fractions accumulated 45Ca2+ during incubation with 0.1 mM 45 CaCl2, buffered with potassium phosphate or glycylglycine (pH 7.5; 28 degrees C). The accumulated 45 Ca2+ was not removable by EGTA, and the uptake was absent at 0 degrees C or after destruction of the particles by sonication. The behaviour of the 45 Ca2+ -uptake into all three fractions against varying ATP-concentrations, metabolic inhibitors (pentachlorophenol, desaspidine, 2,4-dinitrophenol, N-ethylmaleimide, p-chloromercuribenzoate, sodium azide, amobarbital) and drugs (phenoxybenzamine, verapamil, prenylamine, reserpine, bretylium, phentolamine) was studied. Under nearly all conditions there were differences between the 45 Ca2+ -uptake into mitochondria and that into microsomes, which suggests two distinct uptake processes. The 45 Ca2+ -uptake into the granule fraction behaved intermediate between the two other fractions under many conditions, but not under all. Therefore, it is not possible to explain the 45 Ca2+ -uptake into the granule fraction as being due to contamination with mitochondria and microsomes; an inherent ATP-Mg2+ -dependent 45Ca2+ -uptake into the nerve granules must be postulated, which is not directly coupled with the noradrenaline transport into these particles. A particulate fraction (14000-100000 g), containing noradrenaline granules, was prepared from the vas deferens of the rat. Incubation with 5 X 10(-6) M (-)-noradrenaline and 0.1 mM 45Ca2+ showed that the particles of this fraction take up noradrenaline and 45Ca2+. The uptake of both was dependent on ATP-Mg2+. The ATP-Mg2+ -dependent uptake of both noradrenaline and 45Ca2+ was substantially reduced in the corresponding tissue fraction prepared from denervated vasa deferentia.

Chloroquine, quinine, procaine, quinidine, tricyclic antidepressants, and methylxanthines as prostaglandin agonists and antagonists

Chloroquine, quanine, procaine, quinidine, clomipramine, theophylline, and caffeine have been shown to be strong prostaglandin antagonists and weak agonists. The antagonist effect is clearly demonstrable at concentrations reached in human plasma when the drugs are used therapeutically. This suggests that prostaglandins are important in several situations in which their role has hitherto been unsuspected. New approaches to the development of prostaglandin antagonists and new uses for established drugs are indicated. In a preliminary study chloroquine has been successfully used to close patent ductus arteriosus in three infants.

Aspects of the mechanism of action of local anesthetics on the sarcoplasmic reticulum of skeletal muscle

1. The effect was studied of local anesthetics (tetracaine, dibucaine, procaine and xylocaine) on the forward and the backward reactions of the calcium pump of skeletal muscle sarcoplasmic reticulum. 2. The inhibition of the rate of calcium uptake, the rate of calcium-dependent ATP splitting and the rate of calcium-dependent ATP-ADP phosphate exchange by sarcoplasmic reticulum in the presence of the above drugs is at least partially due to the inhibition of the phosphoprotein formation from ATP. 3. The rate of the ADP-induced calcium release from sarcoplasmic reticulum and the rate of ATP synthesis driven by the calcium efflux are inhibited on account of a reduction of the phosphoprotein formation by orthophosphate. 4. The phosphorylation of calcium transport ATPase by either ATP or orthophosphate is diminished by the local anesthetics owing to a reduction in the apparent calcium affinity of sarcoplasmic reticulum emmbranes on the outside and on the inside, respectively. 5. The drug-induced calcium efflux from calcium-preloaded sarcoplasmic reticulum vesicles, a reaction not requiring ADP, is probably not mediated by calcium transport ATPase.

Structure-activity relations for caffeine: a comparative study of the inotropic effects of the methylxanthines, imidazoles and related compounds on the frog's heart

1. The ability of several groups of compounds, related to caffeine, to induce contractures in isolated frog auricular trabeculae has been tested.2. Of the methylxanthines, theophylline, theobromine and paraxanthine are of similar potency to caffeine. This applies to contractures produced in either high-potassium or in sodium-free solution, and to the twitch responses in normal Ringer.3. Xanthines in which the 9-position nitrogen is combined and is, therefore, without an ethylene bond do not affect contraction.4. The hypothesis is put forward that a double-bonded nitrogen, in an imidazole ring, is required for activity of the methylxanthine. This hypothesis is supported by the ability of imidazole and several close derivatives (e.g. histamine), as well as imidazolines, to evoke contractures. As predicted by the hypothesis, imidazolidines and imidazolidones, in which all the nitrogen atoms have single bonds, fail to initiate tension development.5. The activity of histamine and histidine is only demonstrable at high pH ( bumpy equals, equals 9.0).6. Raising the pH in sodium-free solution induces a transient contracture.7. Several arguments suggest that cyclic AMP is probably not an intermediate in the response to the methylxanthines. The activity of cyclic AMP (and adenosine) in eliciting contractures is predicted by the hypothesis because they contain an imidazole moiety as part of their molecular structure.

Lysosomal physiology in Tetrahymena. 3. Pharmacological studies on acid hydrolase release and the ingestion and egestion of dimethylbenzanthracene particles

The ingestion of (14)C-labeled 9,10-dimethyl-1,2-benzanthracene particles, the extracellular release of acid phosphatase, ribonuclease, and alpha-glucosidase, and the egestion of preingested dimethylbenzanthracene particles by Tetrahymena taken from logarithmically growing cultures and resuspended in a dilute salt solution were followed in the presence of several pharmacologic agents. Serotonin, caffeine, and, to a lesser extent, dibutyryl cyclic AMP increased the rate of particle ingestion, but did not alter the rate of release of the three acid hydrolases studied. Added catecholamines did not affect either particle ingestion or acid hydrolase release, but particle ingestion was inhibited by the catecholamine antagonists, dichloroisoproterenol, desmethylimipramine, reserpine, and phenoxybenzamine. These drugs also increased the release of acid phosphatase and ribonuclease in 5-h incubations. Desmethylimipramine acted within 1 h to increase acid hydrolase release, but the effect of dichloroisoproterenol developed more slowly and was secondary to a change in cellular content of the hydrolases. Desmethylimipramine increased the energy of activation for the release of acid phosphatase, while dichloroisoproterenol did not. Both of these drugs enhanced the egestion of preingested dimethylbenzanthracene particles, supporting the view that acid hydrolase release occurs through a cytoproct egestion mechanism. Particle ingestion was also inhibited by colchicine, vinblastine, and cytochalasin B, but these agents had no effect on acid hydrolase release, thus further differentiating the properties of the ingestion mechanism from those of the egestion mechanism. It appears that both microtubules and microfilaments play a role in the ingestion process and that this process may be controlled in part by a cyclic AMP-mediated serotoninergic and adrenergic system.