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PubMed1983

Calcium action potentials in rat fast-twitch and slow-twitch muscle fibres.

Slow action potentials were evoked in twitch fibres of rat extensor digitorum longus (e.d.l.) and soleus muscles after drastically reducing the Cl and K conductances of the muscle fibres. Cl conductance was eliminated by exposing the muscles to a Cl-free saline in which methanesulphonate replaced Cl. K conductance was reduced by adding tetraethylammonium (TEA) and 3,4-diaminopyridine (3,4-DAP) to the Cl-free saline or by overnight incubation of the muscles in a saline containing Cs and TEA. The delayed rectifier was markedly blocked by TEA and 3,4-DAP. In contrast, the inward rectifier was blocked only by TEA. Depolarization with pulses of increasing amplitude triggered slow responses which had a threshold of -30 to -10 mV and a peak amplitude of 50-60 mV. In e.d.l. muscles the time course of the response was sustained for the duration of the pulses and was not affected by repeated stimulation. In soleus muscles the first evoked response was sustained in about 60% of the fibres and transient in the rest. Transient responses reached a peak amplitude and were followed by a hyperpolarization. Repeated stimulation irreversibly transformed the sustained responses of soleus fibres into transient ones. The responses were blocked when the Ca in saline was replaced by Mg (10 mM) or Co (5 mM) or by the addition of Cd (0.1-1.0 mM) or nifedipine (5-6 microM). Tetrodotoxin did not affect the responses. These results strongly suggest that Ca is the main carrier of current during the response. Nifedipine blocked both the Ca response and the subsequent hyperpolarization, suggesting that the latter is due to the activation of a Ca-dependent K conductance.

4-Aminopyridine↗
PubMed1986

Inactivation of calcium channel current in rat uterine smooth muscle: evidence for calcium- and voltage-mediated mechanisms.

Ca channel currents were recorded in Cs-loaded myometrial strips from pregnant rats after addition of tetraethylammonium chloride and 4-aminopyridine (10 mM each) by means of a double sucrose-gap technique. During a depolarizing pulse, the decay of Ca channel current was slowed down when external Ca was replaced by Ba or Sr. This decay represented an inactivation phenomenon, as assessed by the decreased amplitude of inward tail currents following progressively longer depolarizations, the absence of shift in peak conductance curves against membrane potential, and the stable value of the reversal potential when Ba current was increased during conditioning pulses. Inactivation of Ca and Ba currents through Ca channels was studied using the double-pulse method. Conditioning pulses that produced maximal Ca current induced maximal inactivation; with stronger depolarizations, inactivation decreased but was not completely prevented at the expected Ca reversal potential. Increasing the amount of Ca entering the cell during the pre-pulse reduced both amplitude and kinetics of test Ca currents. These results were not observed with Ba as charge carrier suggesting the participation of different mechanisms in inactivation. With Ca as charge carrier, increasing the external Ca speeded the rate of inactivation. This was not observed with Ba outside. Addition of Co (2.5 mM) reduced the amplitude of both Ca and Ba currents but slowed the inactivation of only the Ca current. Recovery from inactivation was described as a two-exponential process only when the conditioning pulse elicited a Ca inward current. In all other cases, recovery from inactivation was represented as a single exponential curve. It is suggested that inactivation of Ca channels in rat uterine smooth muscle is mediated by both internal Ca-dependent and potential-dependent mechanisms.

4-Aminopyridine↗
PubMed1992

The inward rectifier K+ current underlies oscillatory membrane potential behaviour in bovine pigmented ciliary epithelial cells.

1. Fresh bovine, pigmented ciliary epithelial cells possess an inward rectifier current activated by hyperpolarization. This current was investigated using whole-cell patch-clamp techniques. At the holding potential of -70 mV, and with EK (potassium equilibrium potential) set at -84 mV, a small outward current flowed through the inward rectifier that was sensitive to external K+, becoming more outward in 0.5 mM K+ and progressively more inward in 20 and 50 mM K+. 2. The inward rectifier showed V-EK dependence; increasing [K+]o increased the inward conductance from 1.28 nS in 5 mM K+ to 7.42 nS in 50 mM K+. The conductance at a given V-EK was proportional to the square root of [K+]o. 3. It was blocked by external Cs+ but replacing K+ in the pipette with Cs+ blocked only outward ion movement through the inward rectifier. Inward rectification was also blocked by Ba2+ (85% with Ki (concentration giving half-maximal inhibition) = 3.1 x 10(-5) M) and TEA+ (74% with Ki = 2.9 x 10(-4) M). 4. The activation time constant was voltage dependent, decreasing from 5 ms to 0.7 ms over the voltage range -90 to -170 mV. With increasing hyperpolarization the current exhibited time-dependent decay. The time constant for this process was voltage sensitive but the steady-state inactivation was independent of external [K+]. 5. The current disappeared in culture within 8 days. 6. Solution flow over the cell inactivated the inward rectifier, a property that may be related to [K+]o. 7. In current clamp the cells exhibited an unstable region at a potential of around -70 mV. Once in this region oscillations and regenerative hyperpolarizing potentials were observed. This behaviour was eliminated by treatments that blocked (Cs+, Ba2+) or removed (0.5 mM K+) active inward rectification. 8. It is suggested that these oscillations may represent a process of cation loading, the first step in the secretion of aqueous humour.

Animals↗
PubMed1996

Investigating inflammatory bowel disease--white cell scanning, radiology, and colonoscopy.

OBJECTIVE: To evaluate different methods of examination of the bowel in suspected inflammatory bowel disease. DESIGN: Prospective investigation of all children over a three year period with suspected inflammatory bowel disease. A technetium-99m-HMPAO labelled white cell scan (Tc-WCS), barium follow through examination (Ba-FT), and colonoscopy plus biopsy were undertaken. SETTING: Great Ormond Street Hospital for Children, London. SUBJECTS: 39 children (20 male and 19 female), median age 12.1 years (range 3.9-15.1 years). MAIN OUTCOME MEASURES: There was total agreement in 21/39 cases, positive in 16, and negative in five. Of 31 histologically proved cases, positive results were obtained in 28 Tc-WCSs (sensitivity 90%), 10 of 24 Ba-FTs (sensitivity 42%), and 27 colonoscopies (sensitivity 87%). CONCLUSION: The Tc-WCS is sensitive, specific, and non-invasive and should be a first line investigation. Ba-FT with a high radiation burden and relatively low sensitivity requires its role to be redefined. Colonoscopy, with endoscopic biopsy, has a high pick-up rate where facilities and expertise exist.

Adolescent↗
PubMed1989

Continuous membrane voltage recordings in A10 vascular smooth muscle cells: effect of AVP.

Continuous membrane voltage (V) recordings were obtained in A10 vascular smooth muscle cells (rat aorta) using glass microelectrodes. Resting membrane voltage in 262 impalements averaged 54.0 +/- 0.4 (SE) mV. Relative K+ conductance was characterized, and the contribution of electrogenic Na+-K+-ATPase to membrane voltage was investigated. Action potentials could be induced by application of 1 mM barium or 10(-4) M acetylcholine. In a few recordings, spontaneous spike activity occurred, and this could be abolished by 5 mM MgCl2 or by removal of extracellular Ca2+. Barium-induced action potentials were not dependent on the presence of extracellular Na+ and not inhibitable by 10(-6) M tetrodotoxin. Application of 10(-6) M [Arg8] vasopressin (AVP) for 30 s caused a typical biphasic membrane voltage response with an initial transient hyperpolarization of -9.5 +/- 1.1 mV and a more sustained subsequent depolarizing response averaging 28.2 +/- 1.3 mV (mean +/- SE, n = 58). The effect of AVP on membrane voltage was blocked by the V1-antagonist [beta-mercapto-beta,beta-cyclopentamethylenepropionyl1,O-Me- Tyr2,Arg8]vasopressin. The initial hyperpolarizing component of the membrane voltage response to AVP became more prominent when V was predepolarized, for example, by a preceding AVP application. However, when AVP was applied during high K+ depolarization or in the presence of quinidine (1 mM), the initial hyperpolarizing response was practically abolished. The time course of the initial hyperpolarization was shown to be similar to the calcium transient observed in fura-2-loaded A10 cell suspensions after the application of AVP. We conclude that the initial AVP-induced hyperpolarization in A10 cells corresponds to an activation of Ca2+-activated K+ channels.

Acetylcholine↗
PubMed1992

Ionic currents of the lateral pyloric neuron of the stomatogastric ganglion of the crab.

1. The lateral pyloric (LP) neuron is an important component of the network that generates the pyloric rhythm of the stomatogastric ganglion (STG) and is a direct target of many modulatory inputs to the STG. Our aim in this and the subsequent two papers is to describe the conductances present in this cell and to understand the role these conductances play in shaping the activity of the neuron. 2. LP neurons were studied in two-electrode voltage clamp (TEVC) in a saline solution containing tetrodotoxin (TTX) and picrotoxin (PTX) to isolate them pharmacologically from presynaptic inputs. 3. We identified six voltage-dependent ionic conductances. These include three outward currents that resemble a delayed rectifier current, a Ca(2+)-activated K+ current and an A-current similar to those seen in many other preparations. LP neurons show three inward currents, a fast TTX-sensitive current, a hyperpolarization-activated inward current, and a Ca2+ current.

4-Aminopyridine↗
PubMed1994

Characterization of K+ and Ca2+ ionic currents in glomerulosa cells from human adrenal glands.

Ionic currents of primary cultured glomerulosa cells from human adrenal glands were studied with the patch-clamp technique. Two types of outward K+ currents and two types of inward Ca2+ currents were described. The transient outward K+ current activated at potential positive to -40 mV and demonstrated a marked time-dependent inactivation. It was blocked by 4-aminopyridine but not tetraethylammonium. A second type of outward current activated rapidly at the depolarization onset and then increased slowly with no time-dependent inactivation. The transient inward T-type Ca2+ current was activated for potential positive to -60 mV with a maximal current amplitude at -30 mV and zero current voltage at +40 mV; it was completely inactivated for membrane potential positive to -40 mV. The pharmacological studies of the T-type channel showed that Ni2+ was a potent blocker but that the channel was not sensitive to dihydropyridine. The long-lasting inward Ca2+ current was activated for potentials positive to -20 mV with a maximum current amplitude at +70 mV. This current was increased by the agonist Bay K 8644 and blocked by the antagonist nifedipine; in addition, it was blocked by Cd2+ but less sensitive to Ni2+. This study revealed that glomerulosa cells from human adrenal demonstrated the presence of K+ and Ca2+ currents similar to those found in rat and bovine cells. Moreover, the main stimuli of aldosterone secretion, ACTH and angiotensin II, induce an increase in aldosterone secretion which is inhibited in a Ca(2+)-free external medium.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2004

[Effect of coexisting metals on determination of lead and cadmium in the plastic materials test of the Japanese Food Sanitation Law].

The effect of coexisting metals in a sample on the determination of lead and cadmium in plastics used for food contact materials was investigated. In the official method specified in the Japanese Food Sanitation Law, contents of lead and cadmium are determined by a dry incineration method using sulfuric acid. It was assumed that sometimes, coexisting metals in a sample may form insoluble sulfate and that lead sulfate might be adsorbed into the insoluble sulfate. Therefore, hydrochloric acid was added to the ash, to turn formed insoluble sulfate into soluble compounds (HCl addition method). We found that recoveries of cadmium were not affected in the presence of other metals except when calcium exceeded 20 mg/g in both methods. Recoveries of lead decreased in the presence of barium exceeding 0.1 mg/g or calcium exceeding 10 mg/g in the official method. However, improvement of recoveries was achieved with the HCl addition method and by reducing the sample amount to one-tenth (0.1 g) of that specified in the official method.

Barium↗
PubMed1996

Schizostatin, a novel squalene synthase inhibitor produced by the mushroom, Schizophyllum commune. II. Structure elucidation and total synthesis.

Schizostatin (1) has been isolated as a potent and selective inhibitor of squalene synthase. Its structure has been determined using spectroscopic methods: the compound is shown to be a diterpenoid which has a trans-dicarboxylic acid moiety. Total synthesis of schizostatin (1) was achieved by the highly regio- and stereoselective coupling reaction of an allylic bromide with a barium reagent. The Z-isomer 16 was also prepared using the stereoselective syn-addition of an organocopper reagent to acetylenedicarboxylate.

Enzyme Inhibitors↗
PubMed1980

Potassium-induced relaxation of the rat anococcygeus muscle.

The nature of K-induced relaxations of the isolated rat anococcygeus muscle was studied in Tyrode's solution containing a variety of smooth muscle stimulants. When the tone of the preparation was raised by ACh (1 X 10(-6) M), the inhibitory responses to excess K (20-50 MM) were almost completely prevented by tetrodotoxin (1 X 10(-6) M) but not affected by ouabain (2 X 10(-4) M). When the preparation was contracted by barium (5 X 10(-3) M), tetraethylammonium (3 X 10(-2) M) or procaine (8 X 10(-3) M), relaxations by excess K (10-60 mM) were not affected by tetrodotoxin but completely inhibited by ouabain. It is concluded that two types of K-induced relaxations can occur depending on the smooth muscle stimulant used for elevating the tone of the preparation: the one is due to an activation of the electrogenic Na pump mediated by Na+, K+ ATPase of the smooth muscle membrane, the other is due to a stimulation of the inhibitory nerves by K.

Animals↗
PubMed1983

[Synthesis and pharmacological properties of alkyl esters of various DL-omega-phenylamino acids].

The synthesis of some branched-chain and n-alkyl ester hydrochlorides of DL-2-phenylglycine, DL-3-phenyl-3-aminopropionic acid, DL-4-phenyl-4-aminobutyric acid, DL-phenylalanine and DL-4-phenyl-2-aminobutyric acid is described. For 28 alkyl esters of these DL-amino acids, the pharmacological data about the antagonism against spasms induced by barium chloride, histamine and acetylcholine in the guinea-pig ileum in vitro, as well as about the acute toxicity of intraperitoneally administered doses in the mouse, are reported. Empirical structure-activity relationships established for 36 compounds of this group of substances are discussed. It was found that the maxima of the four actions mentioned depended upon the length of the carbon chain in the molecule. In contrast, no clear-cut branching effect was observed. With reference to toxicity, DL-4-phenyl-2-aminobutyric acid n-octyl ester hydrochloride has been found to be the most favourable spasmolytic agent among the compounds under investigation.

Amino Acids↗