An actin-interacting heptapeptide in the cofilin sequence

Cofilin, a 21-kDa actin-binding protein, has a hexapeptide sequence DAIKKK which is identical to the N-terminal portion (residues 2-7) of tropomyosin. The synthetic heptapeptide, DAIKKKL, corresponding to residues 122-128 of cofilin, inhibited the binding of cofilin to F-actin in a dose-dependent manner. The heptapeptide cosedimented with F-actin, decreased the fluorescence intensity of pyrene-labeled F-actin, and increased the rate of polymerization of G-actin. The hexapeptides, DIKKKL and DAIKKL, also inhibited the binding of cofilin to F-actin and affected the fluorescence intensity of pyrene-labeled F-actin and the rate of actin polymerization, like the heptapeptide. However, their effects were weaker than those of the heptapeptide. Moreover, the pentapeptide, DIKKL, had little or no effect. These results suggest that the heptapeptide sequence is specific for the interaction with actin and, therefore, may constitute part of the actin-binding domain of cofilin.

Correlation between somatosensory evoked potentials and sensory disturbance in stroke patients

Somatosensory evoked potentials (SEP) were recorded in 125 (n = 151) stroke patients more than 3 weeks after disease onset and in 55 healthy adults. The correlation between sensory disturbance, N20 amplitude ratio, and the central conduction time (CCT) was then investigated. N20 amplitude ratio was given by the amplitude of the affected side divided by that of the unaffected side and presented as a percentage, while CCT represents the time interval between N20 and N13. For the healthy subjects, normal values of CCT were 6.1 +/- 0.4 msec (20-59 years old) and 6.4 +/- 0.4 msec (over 60 years old). Normal amplitude ratios were left side/right side = 97.5 +/- 16.4% and right side/left side = 105.4 +/- 17.7% with the value at the second standard deviation, 64.7%, representing the normal range of the amplitude ratio. Of 98 stroke patients with an abnormal amplitude ratio and 23 with an abnormal CCT, 91.8% and 95.7%, respectively, had sensory disturbance. Conversely, 82.6% of those with sensory disturbance showed an abnormal amplitude ratio, while only 38.6% with sensory disturbance showed an abnormal CCT. There was a definite correlation between sensory disturbance and either CCT or amplitude ratio, however, there was none between CCT and amplitude ratio. On the basis of these results, we concluded that amplitude ratio would be more effective than CCT as a parameter for monitoring sensory disturbance in stroke patients.

Cardiovascular actions of buflomedil and possible mechanisms involved

Cardiovascular effects of buflomedil (Bufedil) were studied in dogs, rabbits and guinea pigs. 1. In pentobarbital-anesthetized dogs, buflomedil (0.32-5.12 mg/kg i.v.) induced a dose-dependent fall of blood pressure and a slight increase of heart rate at 0.32-1.28 mg/kg but a heart rate decrease at 2.56 and 5.12 mg/kg. 2. Buflomedil administered into the maxillary (10-320 micrograms/kg), internal carotid (40-320 micrograms/kg) and vertebral artery (20-640 micrograms/kg) increased respective blood flows dose-dependently. 3. Buflomedil (i.v.) also produced dose-dependent increases of the maxillary blood flow at 0.08-0.64 mg/kg, internal carotid flow at 1.28-5.12 mg/kg and vertebral flow at 0.32-5.12 mg/kg, respectively. These increasing effects were attenuated at larger doses because of marked hypotension. 4. Buflomedil (10 mg/kg i.v.) reduced pressor responses to norepinephrine (noradrenaline) and enhanced depressor responses to isoprenaline (isoproterenol), without affecting depressor responses to acetylcholine and positive chronotropic responses to norepinephrine and isoprenaline. 5. After buflomedil (i.v.), the femoral and coronary blood flow increased dose-dependently while renal blood flow decreased. These increasing effects were also reduced at larger doses because of hypotension. 6. Buflomedil (i.v.) induced a dose-dependent increase of cardiac output at 0.16-0.64 mg/kg, biphasic changes at 1.28 and 2.56 mg/kg and a marked decrease and subsequent slight increase at a large dose of 5.12 mg/kg. 7. 4-Desmethylbuflomedil (i.v.); elicited dose-dependent biphasic changes of blood pressure at 0.64-5.12 mg/kg, and a slight increase of heart rate at 0.32-2.56 mg/kg but decreases at 5.12 mg/kg. It also elevated, dose-dependently, the maxillary blood flow at 0.16-5.12 mg/kg and vertebral flow at 1.28-5.12 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of 1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl) ethanol and possible mechanisms involved

Cardiovascular effects of NC-1100 (1-(3,4-dimethoxyphenyl)-2-(4-diphenylmethylpiperazinyl)ethanol and possible modes of action were studied in dogs and guinea pigs. 1. In pentobarbital-anesthetized dogs, intravenous administration of NC-1100 (0.05-1.6 mg/kg) induced a dose-dependent fall of blood pressure, a bradycardia followed by temporal tachycardia, a slight and transient stimulation of respiration and a prolongation of the R-R interval with slight augmentations of P, R and T waves in ECG. 2. In pentobarbital-anesthetized dogs, NC-1100 (2.5-80 micrograms/kg) administered to the maxillary and vertebral artery dose-dependently increased the blood flow in the respective artery. 3. Intravenous administration of NC-1100 (0.05-1.6 mg/kg) also exhibited dose-dependent increases of the maxillary and vertebral blood flow, though the increase in maxillary flow was a little reduced at a high dose of 1.6 mg/kg. Intravenous administration of NC-1100 (0.1-1.6 mg/kg) caused a slight increase in the aortic and coronary blood flow, a decrease in renal flow and a slight and transient decrease followed by an increase in femoral flow. 4. In pentobarbital-anesthetized dogs, NC-1100 (1 mg/kg) administered i.v. did not affect responses of blood pressure and heart rate to norepinephrine and isoprenaline (isoproterenol) but slightly inhibited hypotensive responses to acetylcholine. NC-1100 had no effect on hypertension elicited by carotid sinus reflex and on bradycardia by vagus stimulation. NC-1100 slightly inhibited the tachycardia elicited by pre- as well as postganglionic stellate stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity purification of a 65-kilodalton parasporal protein from Bacillus thuringiensis PG-14 that shows mosquitocidal activity

By using antibody-mediated affinity chromatography, a highly mosquito larvicidal but nonhemolytic fraction was obtained from alkali-solubilized, silkworm (Bombyx mori) larval gut juice-treated parasporal inclusions of Bacillus thuringiensis strain PG-14 (serotype 8a:8b). This fraction contained a 65-kDa protein only but not a 25-kDa protein, the main component in the flow through fraction unbound to the affinity column. The 25-kDa protein purified from the unbound fraction by CM-cellulose chromatography demonstrated a high hemolytic activity against sheep red blood cells but very low mosquito larvicidal activity.

Protein import into yeast mitochondria is inhibited by antibodies raised against 45-kd proteins of the outer membrane

Import of several precursor proteins into isolated yeast mitochondria is inhibited by rabbit antiserum raised against the total mitochondrial outer membrane or against electrophoretically purified 45-kd outer membrane proteins. Antisera against other outer membrane proteins are only marginally active or inactive. Inhibition by the antiserum against 45-kd proteins is only weak with untreated mitochondria, but reaches 80-90% with mitochondria that had been pretreated with 0.1 mg/ml trypsin. This trypsin pretreatment by itself inhibits precursor import only slightly (30-50%). Selective inhibition of import does not correlate with binding of the various IgGs to the mitochondrial surface and is also observed with the corresponding Fab fragments. Inhibition by antibodies against 45-kd outer membrane proteins strongly suggests the existence of a mitochondrial surface protein mediating protein import and offers a means of isolating this protein.

Disruption of the outer membrane restores protein import to trypsin-treated yeast mitochondria

Treatment of isolated yeast mitochondria with high levels (1 mg/ml) of trypsin severely inhibits protein import but does not destroy the integrity of the outer membrane or abolish mitochondrial energy coupling. If the outer membrane of these trypsin-inactivated mitochondria is disrupted by osmotic shock, the resulting mitoplasts are again able to import proteins. Protein import into mitoplasts, like that into intact mitochondria, is energy-dependent; however, whereas import into mitochondria is inhibited by antibody against 45-kd proteins of the outer membrane [Ohba and Schatz, EMBO J., 6, 2109-2115 (1987)], import into mitoplasts not affected by this antibody. Protein import into mitoplasts appears to bypass one or more steps normally occurring at the mitochondrial surface.

Behavioural assessment as substance P antagonists in mice

A series of eleven undeca- and four hexapeptide antagonists of substance P (SP) have been assayed by the SP-induced behavioural test in mice. When 2 nmol of [D-Arg1, D-Pro, D-Trp, Leu]-SP (SP 1-11 I) was intrathecally injected together with SP (0.1 nmol), SP-induced response which consists of scratching, biting and licking was markedly inhibited. [D-Trp, Leu]-SP 6-11 (SP 6-11 I) given in a dose of 2 nmol was also inhibited the SP-induced response to the same degree as SP 1-11 I. Some of SP 1-11 or SP 6-11 analogues substituted with fluorine in positions 7 and/or 8 maintained the antagonistic effect of SP 1-11 I or SP 6-11 I, though the others were weaker. Intrathecal administration of SP 1-11 I and SP 6-11 I resulted in long-lasting antinociceptive effects as measured by the tail-flick test. Fluorine-containing SP analogues were less potent than the above two analogues in producing antinociception. These results suggest that the antagonistic effect of SP analogues on the SP-induced nociceptive response do not necessarily relate to antinociceptive activity at the spinal cord level.

Plasma levels and urinary excretion of batroxobin and its defibrinogenating effects in various animal species

The plasma levels and urinary excretion of batroxobin administered to 6 species of animals were examined by an enzyme immunoassay method. Defibrinogenating effect of batroxobin was also studied in those species. The plasma levels of immunoreactive batroxobin disappeared exponentially in all the animals and differences in half-life were observed to occur according to species. The elimination half-life of immunoreactive batroxobin in the plasma was the largest in dogs, followed by rats, monkeys, guinea pigs, mice and rabbits. The extent of the defibrinogenating effect was also noted to vary according to the species, being greatest in dogs and then monkeys, mice, rats, guinea pigs and rabbits. Following the continuous infusion of batroxobin into dogs, its level in the plasma remained high over a considerable period of time and the defibrinogenating effect lasted in corresponding to its plasma level. The urinary excretion of immunoreactive batroxobin was quite small in these species, being 0.2-1.9% of the original dose.

Effects of tonicity on the pacemaker activity of guinea-pig sino-atrial node

Spontaneously beating sino-atrial node (S-A node) of guinea-pig was superfused with solutions of various osmolarities. The changes in the rate of spontaneous beating and in action potentials were measured. In the solution of normal tonicity, the rate of spontaneous beating was 214 +/- 6 beats/min (mean +/- S.E.) and the maximum rate of rise was 9.7 +/- 2.5 V/s. When extracellular Na+ was reduced by 33%, isotonically replaced with sucrose, the heart rate was reduced to 177 +/- 8 beats/min and the maximum rate of rise was reduced to 7.6 +/- 1.2 V/s. Decreasing the osmolarity by 30% increased the heart rate by 6% and increasing the osmolarity to 130, 150, and 170% decreased the heart rate to 94, 89, and 73%, respectively, in low Na+ medium. The tonicity dependence of the heart rate was not affected by TTX, atropine, phentolamine, or propranolol. When the tonicity was either increased twice or decreased half, the spontaneous beating stopped. Adding either K+ or Rb+ of 6 mM to the solution which was two times as hypertonic as the normal, could activate the beating again. Substances inhibiting the potassium conductance such as tetraethylammonium (TEA), 4-aminopyridine (4-AP), and cesium chloride (CsCl) could also reactivate the spontaneity. Although lowering extracellular Ca2+ concentration could reactivate the spontaneity in the hypertonic medium, increasing Mg2+ inhibited the reactivation. The contribution of K+ current in the effects of changing osmolarity on the spontaneous beating is discussed.

Mechanism of inotropic action by hypotonic solution in the frog atrial muscle

The effects of hypotonic solution on the mechanical activities and action potential of the bullfrog atrium were investigated. Exposure of muscle to hypotonic solutions (70% of normal solution) produced initially a transient increase in twitch after which twitch declined below the control level. The response is independent of the kinds of salts withdrawn to make the medium hypotonic and of the presence of beta-blocker (5 X 10(-7) M propranolol). The resting potential and the plateau level of action potential were little changed initially. When the twitch declined, a small amount of depolarization and a shortening of action potential duration were observed; however, the plateau level of action potential was not reduced. The initial increase in twitch was not observed, and only the gradual decline of twitch remained in the caffeine containing hypotonic solution. The weight of muscle increased 10% in the hypotonic solution. The resting tension was also increased transiently and then declined to reach a maintained plateau with exposure to hypotonic solution. In the 0-Ca2+ or caffeine containing medium, the transient component of contracture was suppressed but the plateau tension remained. It is suggested that the initial transient increase of twitch by the perfusion of the hypotonic solution was induced by the Ca2+ released from the sarcoplasmic reticulum (SR), and the resultant decline of twitch resulted from the depletion of Ca2+ from the SR and/or from the shortening of action potential duration.

A role of ionic strength on the inotropic effects of osmolarity change in frog atrium

The influence of varying the ionic strength of the bathing solution on the contraction of chemically skinned frog atrial muscle fibers was studied. The rate of tension development activated by calcium slows as the ionic strength is elevated. The size of caffeine contracture, however, was larger in the fiber preloaded with calcium at a higher ionic strength. There was a decrease in the maintained tension at 10(-6) M Ca when a fiber was bathed in a high ionic strength solution. Returning to a normal ionic strength solution caused a transient tension increase. When the fiber was bathed in a low ionic strength solution, the maintained tension increased transiently to a high value and then declined to reach a plateau. The response was also observed in a solution of pCa 8. In the caffeine-treated fiber or in the fiber bathed in ATP free solution, although the maintained tension level was changed corresponding to the altered ionic strength, the transient responses were blocked. These responses were not much influenced by the kinds of salts used to change the ionic strength. When osmolarity of the medium was altered by sucrose, transient responses were not induced. The results could qualitatively explain the isometric tension change of an intact fiber of frog atrium bathed in a hyper- or hypotonic solution.

Calcium antagonistic action involved in vasodilation by brovincamine

Possible mode of vasodilative action of brovincamine was assessed in isolated cardiovascular preparations in comparison with verapamil and papaverine. Brovincamine (IC50: 1.2 x 10(-5) M), verapamil (IC50: 3.5 x 10(-7) M) or papaverine (IC50: 2.5 x 10(-5) M) caused a dose-dependent relaxation of potassium (30 mM)-contracture in the rabbit pulmonary arterial segment. This relaxation by verapamil or brovincamine, but not by papaverine, was antagonized by increasing external Ca2+ concentration to 12.4mM. Duration of slow action potentials of partially depolarized guinea-pig papillary muscle was reduced by 14 min exposure to brovincamine (5 x 10(-5) M) or verapamil (10(-5) M. These results suggest that brovincamine produces a vasodilation via a slow Ca2+-channel blockade.

A study on the mechanism of twitch potentiation by hypertonic solution in the frog atrial muscle

Hypertonic solutions were found to exhibit both positive and negative inotropic effects on the contraction of the isolated atrial myocardium of bullfrog. The optimum tonicity for twitch potentiation was about 1.5 T. The mechanism for the positive inotropic action was investigated. The possibility of involvement of an increase in calcium influx during each action potential was excluded, since both the overshoot and the plateau of action potential were strongly depressed by perfusion of hypertonic solution. The effect on the time course of twitch potentiation was similar to that of muscle shrinkage, regardless of the type solute (sucrose, NaCl or LiCl) used for elevating the tonicity, except that excess sodium showed an initial rapid inhibitory phase of contraction. A marked post-rest potentiation was observed even after "zero" calcium perfusion, provided that the tonicity of the bathing medium was elevated previously. Potassium contracture occurred during the prolonged hypertonic perfusion in "zero" calcium condition. In addition, caffeine contracture was strongly augmented in hypertonic solution. The results suggest that an elevation in both the [Ca2+]i and amount of calcium bound intracellularly may play an important role in the positive inotropic action.

Paradoxical after-potentiation of the myocardial contractility by lanthanum

Lanthanum of 0.1 to 0.2 mM caused a twitch inhibition and further showed a marked, long-lasting twitch potentiation during washout in both ventricular strips of bullfrog and atrial or papillary muscles of guinea-pig. It was found that the effect was more conspicuous in the frog heart. A similar potentiation was observed by applying gadolinium instead of lanthanum. The participation of endogeneous catecholamine release is unlikely since the positive inotropic effect was never affected by the presence of beta-adrenergic blocker. The potentiation was not accompanied by any increase in the action potential plateau, suggesting independence of the phenomenon on the calcium current. A marked elevation of the resting tension was produced during a long-term lanthanum perfusion, reflecting the increase in the intracellular calcium level. On the other hand, transient increase in the resting tension was frequently observed on returning to normal Ringer solution. The latter change seemed to result from a transient increase in the resting permeability to calcium ions. The negative or positive inotropic effect by increasing or lowering the external sodium concentration observed under the control condition was strongly depressed during the twitch potentiation. In addition, sodium-free contracture induced by solutions isotonically replaced with sucrose or potassium chloride was augmented both during lanthanum perfusion and during its washout. These results suggest the possibility that the elevation of the intracellular calcium level due to inhibition of Na-Ca exchange mechanism and/or increase in the calcium permeability is the principal cause for the twitch potentiation caused by lanthanum washout.

Autonomous control of the level of methylation of methyl-accepting chemotaxis protein

Methylation and demethylation of the methyl-accepting chemotaxis protein (MCP) was studied in vitro. The in vitro MCP methylating system showed the following characteristics. 1. Multiple bands of methylated MCP were produced. 2. The reaction could be separated into two phases: the initial phase, in which the level of methylation increased as a result of multiple methylation; and the stationary phase, in which methylation and demethylation took place at the same velocity without apparent change in the level of methylation. 3. Pulse-chase analysis of the reaction showed that MCP was demethylated preferentially at the relatively highly methylated state. 4. The behavior of MCP in this system was similar to that of MCP stimulated in vivo with attractant. Based on the above results, an autonomous control mechanism of the level of MCP methylation is discussed.

Immobilization of the periplasmic maltose-binding protein of Escherichia coli

Easy and rapid procedures for immobilization of the periplasmic maltose-binding protein was worked out. The matrix was able to adsorb a maltose-chemosensing component, methyl-accepting chemotaxis protein of tar pathway. The adsorption was not seriously affected by the presence of other chemicals in tar pathway such as aspartate or nickel ion.

An in vitro study of the methylation of methyl-accepting chemotaxis protein of Escherichia coli. Construction of the system and effect of mutant proteins on the system

An in vitro system for the methylation of methyl-accepting chemotaxis proteins (MCP's), which have been shown to be membrane integral proteins, was constructed. The system, consisting of the membrane, the cytoplasm, and labeled S-adenosyl methionine, showed the following characteristics. 1. The methylation of MCP in the membrane required the cytoplasm. The rate of incorporation of the labeled methyl group into MCP was dependent on the amount of the cytoplasm. 2. Incorporation of the labeled methyl moiety into MCP reached a steady state, and the level of the steady state incorporation was dependent on the concentration of the cytoplasm when the concentration of the membrane protein was constant. 3. The methyl moiety which had been incorporated into MCP before the steady state could be exchanged. It was suggested that the amount of methyl group introduced into MCP was equal to that of taken from MCP. 4. The methylated MCP was demethylated faster in the presence of a methyl donor than in its absence. 5. The membranes obtained from cheX-, cheB-, and cheZ mutants were inactive in the present in vitro system even when they were mixed with the wild type cytoplasm.

Negative inotropic effect of beta-blockers in the guinea-pig atrium after preincubation with isoprenaline

In the isolated guinea-pig atrium, pretreated with a high concentration of isoprenaline (8 x 10(-7) M), beta-blockers produced a marked negative inotropic effect in a concentration which by itself was too low to have a direct depressing action. No negative inotropic effect was caused by isoprenaline when beta-blockers were applied first. The depressing action of beta-blockers was unaffected by phentolamine or atropine. During the depression, the electrical parameters of the action potential were not significantly different from those of the control, though the contractions were much smaller than control ones. The negative inotropic effect of beta-blockers was weaker in excess Ca (7.5--10 mM). The observations indicate that isoprenaline possesses a dual action but that the negative inotropic effect is usually masked by the positive inotropic effect and that beta-blockers, by quickly abolishing the positive inotropic effect, reveal the underlying negative inotropic effect.

Measurement and significance of the reversal potential for the pace-maker current (iK2) in sheep Purkinje fibres

1. The apparent reversal potential (Erev) of the pace-maker current (iK2) is found to depend on the experimental protocol used for its measurement. Evidence is presented showing that depolarizing (hyperpolarizing) pulses given before a test hyperpolarization used to determine Erev, shift Erev to more negative (positive) values. These shifts are opposite to those expected if the only effect of pre-pulses were to change the concentration of potassium in extracellular clefts ([K]c) via accumulation and depletion processes. 2. This effect is shown to be due to the fact that Erev is dependent on s0, the degree of activation of iK2 at the start of the test hyperpolarization. 3. When a suitable protocol is used, depletion of cleft K can be demonstrated to take place during a large hyperpolarization. Changes in the level of [K]c induced by pre-pulses must therefore also affect the Erev determination. 4. A simplified three-compartment model has been used to investigate how K accumulation and depletion can affect the time course of iK2, with particular reference to the problem of Erev determination. Computed examples show that the model is able to reproduce the main features of the time course of iK2 recorded near its reversal potential and the changes induced by pre-pulses on Erev measuremnet. By contrast, simulation on a linear cable model rules out the possibility that such results are due to voltage non-uniformity. 5. The three-compartment model predicts that the measured value of Erev differs from EK2 for two reasons: (1) when the recorded current trace is flat iK2 is still outward and decaying, and (2) the K equilibrium potential shifts to more negative values while the test hyperpolarization is applied. 6. The finding that Erev is directly affected by changes in s at the beginning of the test pulse is discussed in relation to the action of agents (such as Ca2+, H+, salicylate, adrenaline and ouabain) which are found to shift both the s00 curve and Erev.

Action of salicylate ions on the electrical properties of sheep cardiac Purkinje fibres

1. In sheep Purkinje fibre preparations, salicylate ions produce reversible changes in resting potential and in action potential duration. In most preparations these effects resemble those produced by -ow extracellular K concentration: the resting potential first increases and then decreases, the action potential is prolonged and eventually, low potential oscillations occur in the plateau range. In a few preparations, action potential shortening occurs. 2. The threshold current for initiating action potentials by an intracellular electrode is reversibly increased by salicylate. 3. The activation curve, soo(Em), for the pace-maker K current, iK2, shifted in a hyperpolarizing direction. The magnitude of the shift is about -5 mV in 5 mM-salicylate and -30 mV in 50 mM-salicylate. 4. The apparent reversal potential for iK2 is shifted in a negative direction. The magnitude of this shift at a given salicylate concent;ation varies with the K concentration. In an extracellular K concentration of 2.7 mM an average shift of -18 mV occurs in 10 mM-salicylate; in 8 mM, the average shift is only -1 mV. 5. It is proposed that most of these effects may be produced by an increase in surface negative potential produced by the binding of salicylate to the cell membrane. This would produce the hyperpolarizing shift of activation curves for ionic current and, by increasing surface K activity, may lead to stimulation of the Na-K pump to produce an increase in the K gradient across the cell membrane.

The interaction of ouabain and salicylate on sheep cardiac muscle

1. The action potential duration in sheep ventricular fibres is rapidly diminished on exposure to 10(-6) M-ouabain. However, if 10--20 mM-sodium salicylate is added to the ouabain solution, glycoside-induced shortening is prevented, and a substantial increase in duration then occurs. Sodium salicylate also reverses the shortening effect of ouabain if applied after the glycoside has been allowed to act alone. 2. Sodium salicylate alone produces a much smaller prolongation than in the presence of ouabain. Alone and in the presence of ouabain it eventually increases the threshold and produces inexcitability. 3. Three other surface charge agents have been compared with salicylate: aminonaphthalene sulphonate, sodium dodecylsulphate and salicylamide, were unable to counter the actions of ouabain at the concentrations used. Since they also produced no changes in excitability it is likely that they did not bind significantly to the cell membrane. 4. In Purkinje fibres the reversal potential for the pacemaker current, iK2, is initially shifted in a negative direction in the presence of 10(-6) M-ouabain and 10 mM-salicylate instead of the positive shift expected with ouabain alone at this concentration. 5. In guinea-pig ventricle, salicylate alone reduces the duration of the action potential. This effect is rapidly reversible. Toxic levels of ouabain also reduce the action potential duration but this effect takes several hours to reverse. By contrast, the effects of salicylate and ouabain applied together are readily reversible. 6. It is suggested that the mechanism of these effects may depend on the ability of a surface negative charge agent like salicylate to increase the surface K+ concentration at the membrane and so protect the sodium-potassium pump from inhibition by large doses of ouabain.

In vivo methylation of elongation factor Tu of Escherichia coli

A protein existing mainly in the supernatant fraction of Escherichia coli was found to be methylated by accepting the methyl moiety originating from methionine. The protein was identified as peptide synthesis elongation factor Tu (EF-Tu) by the following criteria. 1) The methylatable protein separated at the same position as purified EF-Tu on two-dimensional gel electrophoresis. 2) The methylatable protein interacted with antiserum specific for EF-Tu. Amino acid analysis of the methyl-labeled protein suggested that the site of methylation was an epsilon-amino group of lysine.

Studies on bacterial chemotaxis. III. Effect of methyl esters on the chemotactic response of Escherichia coli

The methylation-demethylation reaction of methyl-accepting chemotaxis protein (MCP) is tightly coupled to the appearance of the chemotactic response in Escherichia coli. The bacteria might therefore show a unique response upon the addition of a compound containing a methyl group. We selected methyl N-methyl anthranilate (NMMA) and its analogs for examination. When NMMA was added to a suspension of E. coli (wild type), the bacteria tumbled as it does in the presence of a repellent. NMMA caused tumbling of wild-type bacteria for at least 20 min, while a conventional repellent makes the bacteria tumble for at most one min. The effect of NMMA requires functional MCP, cheA gene product, cheB gene product, and possibly cheX gene product. A positive signal of NMMA (i.e. sudden dilution) was detected by cheZ mutants with much higher sensitivity than that of a conventional repellent, indole, while both signals were rather poorly but equally detected by cheB mutants. These results suggest that the drug is related to the function of cheB gene product, a possible demethylating enzyme of MCP.

The steady state TTX-sensitive ("window") sodium current in cardiac Purkinje fibres

Voltage clamp experiments on isolated sheep Purkinje fibres showed an increase of the steady state outward membrane current, over the potential range -65mV to -15 mV, in the presence of tetrodotoxin (TTX, 3.10(-5 M). This "window" current is considered to be the steady state component of the fast sodium current (INa), resulting from the crossover of the activation and inactivation curves which govern the opening of the sodium channel. TTX had no significant effect on the reversal potential, activation curve, kinetics or instantaneous I-V relationship of the pacemaker current IK2. The window found in these experiments extends to potentials well into the range of the action potential plateau. Consequently small changes of the steady state INa might have large effects on the action potential duration. The effects of TTX and local anaesthetics are discussed in this context.

Mutant and immunochemical studies on the involvement of cytochrome b5 in fatty acid desaturation by yeast microsomes

The involvement of cytochrome b5 in palmitoyl-CoA desaturation by yeast microsomes was studied by using yeast mutants requiring unsaturated fatty acids and an antibody to yeast cytochrome b5. The mutants used were an unsaturated fatty acid auxotroph (strain E5) and a pleiotropic mutant (strain Ole 3) which requires either Tween 80 and ergosterol or delta-aminolevulinic acid for growth. Microsomes from the wild-type strain possessed both the desaturase activity and cytochrome b5, whereas those from mutant E5 contained the cytochrome but lacked the desaturase activity. Microsomes from mutant Ole 3 grown with Tween 80 plus ergosterol were devoid of both the desaturase activity and cytochrome b5, but those from delta-aminolevulinic acid-grown mutant Ole 3 contained cytochrome b5 and catalyzed the desaturation. The cytochrome b5 content in microsomes from mutant Ole 3 could be varied by changing the delta-aminolevulinic acid concentration in the growth medium, and the desaturase activity of the microsomes increased as their cytochrome b5 content was increased. The antibody to yeast cytochrome b5, but not the control gamma-globulin fraction, inhibited the NADH-cytochrome c reductase and NADH-dependent desaturase activities of the wild-type microsomes. It is concluded that cytochrome b5 is actually involved in the desaturase system of yeast microsomes. The lack of desaturase activity in mutant Ole 3 grown with Tween 80 plus ergosterol seems to be due to the absence of cytochrome b5 in microsomes, whereas the genetic lesion in mutant E5 appears to be located at ther terminal desaturase.

Effects of sodium, potassium and calcium ions on the slow wave in the circular muscle of the guinea-pig stomach

1. The contribution of Na, K and Ca ions to the generation of slow waves in the circular muscle of the guinea-pig stomach was studied.2. The slow waves had a lower, potential-independent (first) and an upper, potential-dependent (second) component. Reduction of the external Na prolonged the first component, but complete removal of Na depolarized the membrane and caused deterioration of the slow wave.3. Readmission of Na (5-10 mM) restored the slow wave; this action was not abolished by ouabain.4. Removal of K depolarized the membrane and slightly reduced the amplitude and duration of the slow waves. Readmission of K hyperpolarized the membrane and increased the amplitude and duration of the slow waves, particularly of the first component. Ouabain blocked the effects on the membrane potential, but not the effects on the slow waves.5. An increase in extracellular Ca prolonged the first component and reduced the frequency. Removal of extracellular Ca abolished the slow wave activity. Excess Ca enhanced, and low Ca reduced the effects of altering the concentrations of external K.6. It is concluded that the ouabain-sensitive Na-K pump may not be directly involved in generating slow waves, but that some other metabolic process is involved, which is regulated to a large extent by Ca, and possibly also by Na and K.

Impedance components in longitudinal direction in the guinea-pig taenia coli

1. When the tissue impedance of the guinea-pig taenia coli was measured across a 2 mm sucrose gap in a longitudinal direction, the impedance locus could be fitted by two different circular arcs. Their characteristic frequencies were about 0-6 and 240 Hz after 60 min superfusion with sucrose solution. From the effects of changing the width of sucrose gap and of transection of tissue, and also from taking the difference between impedances measured at two distances, it was concluded that the low-frequency locus corresponds to the transverse impedance of the plasma membrane and the high-frequency locus to the longitudinal tissue impedance. 2. A change in the longitudinal tissue impedance was measured during superfusion with sucrose solution, using a frequency range between 5 Hz and 10 kHz. The admittance decreased with time of superfusion and this time course could be expressed by the sum of three exponential terms. The fastest component, having a time constant of 1-3 min at 10 kHz, was interpreted to correspond to a process of wash-out of extracellular medium. 3. Admittances at zero and infinite frequencies were obtained from the impedance locus. The decrease in these admittances with the time was analysed and the values at the start of washing were obtained by extrapolating the admittance change to zero time. 4. From these values it was estimated that the myoplasmic resistance was 214 omega cm, the junctional resistance 372 omega cm, and the junctional capacity 3-1 muF/cm at 25 degrees C. In these calculations the equivalent circuit of tissue was assumed to be expressed by two components in series: one for the myoplasmic resistance and the other for the junction which has the junctional resistance and capacity in parallel. 5. After 90 min superfusion with sucrose solution, the total tissue impedance measured at zero frequency was increased from 586 to 3034 omega cm. In the total impedance the myoplasmic resistance was increased from 214 to 914 omega cm and the junctional resistance from 372 to 2120 omega cm. Thus, the change in junctional resistance was greater than that in myoplasmic resistance during superfusion of sucrose solution.