Use- and frequency-dependent blockade by UL-FS 49 of the if pacemaker current in sheep cardiac Purkinje fibres

The mechanism by which the bradycardiac agent UL-FS 49 blocks the if pacemaker current was investigated in sheep Purkinje fibres using the two microelectrode voltage-clamp technique. If was activated by 1 s pulses applied between -30 mV and -120 mV at 0.4 Hz in a modified Tyrode solution containing BaCl2 and MnCl2, and with TRIS replacing most of the Na+. UL-FS 49 caused an exponential decline of the if current amplitude during a train of pulses. Both the rate and extent of the if reduction increased with drug concentration, without there being a resting blockade. Recovery from blockade followed a single exponential time course during prolonged hyperpolarizations. The recovery rate was extremely slow and increased with more negative voltages, as did the extent of steady state recovery from blockade. A frequency-dependent reduction of the diastolic depolarization rate resulted from a use-dependent blockade of the pacemaker current.

[Protective action of Salvia miltiorrhiza aqueous extract on chemically induced acute myocardial ischemia in rats]

Aqueous extract of Salvia miltiorrhiza (SM-H) can protect the acute myocardial ischemia and arrhythmia of Sprague-Dawley rats induced by isoproterenol (ISO) or BaCl2 with the following results: (1) intraperitoneal injection (i.p.) of SM-H for 3 to 5 days or intravenously (i.v.) just once significantly reduced the death rate of the animals, (2) i.v. SM-H pretreatment significantly increased the lethal dose of BaCl2 infusion, (3) i.p. SM-H significantly decreased premature ventricular contraction, ventricular fibrillation, bradycardia and mortality rate induced by bolus i.v. of BaCl2, and (4) i.p. SM-H also significantly reduced ECG J-point displacement of rats induced by ISO.

A double perfusion system with two-channel recording for the simultaneous study of the contractile responses of the circular and longitudinal smooth muscle layers of the rat vas deferens

A device for double perfusion of the vas deferens externally and through the lumen is described in detail. The perfusion system allows the simultaneous recording of drug-induced or spontaneous contractions of the circular and longitudinal smooth muscle layers of the organ. Isometric contractions of the longitudinal (external) layer are recorded through a tension transducer. The contractions of the circular (internal) smooth muscle layer are recorded as changes of the pressure of internal perfusion. Therefore, four different effects can be recorded for a given concentration of agonist by combining the variables related to the route of perfusion (external or internal) and type of muscle (longitudinal or circular). In addition, antagonism or synergism can be studied by simultaneously perfusing a second drug. Results can be expressed as single records or as mean concentration-response curves from which drug-receptor parameters can be directly or indirectly obtained. The importance of employing this method for the analysis of some less usual problems related to the mechanism of drug action is discussed.

Effects of verapamil on synaptic transmission in mammalian sympathetic ganglia

Effects of verapamil (Ver) on the synaptic transmission of isolated superior cervical ganglia (SCG) were investigated by means of intracellular recording techniques. In the neurons of SCG of rabbits and guinea pigs, Ver (100-400 mumol/L) depressed both the synaptic responses (f-EPSPs and/or evoked action potentials) elicited by orthodromic stimulation and the acetylcholine (ACh) potentials induced by pressure ejection of ACh. 4-Aminopyridine (4-AP, 100 mumol/L) and BaCl2 (5 mmol/L) facilitated the f-EPSPs inhibited by Ver, but had no notable effect on the ACh potentials depressed by Ver. Ver suppressed the ACh potentials enhanced by pyridostigmine (1 mumol/L). The potentiating effect of soman (1 mumol/L) on the ACh potentials was prevented by Ver. It is suggested that Ver can block the synaptic transmission of mammalian SCG by both the pre- and postganglionic mechanisms.

Reversible activation of the ATP-dependent potassium current with dialysis of frog atrial cells by micromolar concentrations of GDP

We studied the effects of internal and external solutions on potassium currents in frog atrial cells. Experiments were carried out in whole cell recording in the presence of tetrodotoxin and cobalt in the bath to suppress the inward currents. In the absence of pyruvate and glucose in the external solution, a time-independent current increased progressively in a few minutes till the death of the cell. This current had the properties of the ATP-sensitive potassium current IK(ATP) in mammalian cells. In the presence of pyruvate and glucose in the external solution, the membrane current stayed low for 30 min. Addition of guanosine monophosphate (GMP, 40 microM), guanosine triphosphate (GTP, 40 to 1000 microM), adenosine diphosphate (ADP, 40 microM) or adenosine triphosphate (ATP, 3000 microM) to the internal solution had no major effect on the current amplitude. In contrast, addition of GDP (20 or 40 microM) produced a loss of rectification in a few minutes. The current activated by GDP was time independent as was the current observed in the absence of glucose and pyruvate. It was sensitive to cesium and barium, it was blocked when ATP was added to GDP in the internal solution, and it was suppressed by the sulphonylurea glibenclamide (1 microM). We suggest that GDP produced a local depletion of ATP, by displacement of the equilibrium between ATP, GDP, ADP and GTP. This hypothesis is supported by the fact that the current activated by GDP was rapidly suppressed when adding GTP in excess to the internal solution.

Membrane hyperpolarization is a mechanism of endothelium-dependent cerebral vasodilation

Acetylcholine (ACh)-induced hyperpolarization of cerebral arteries requires a functional endothelium. The hyperpolarization is reversed by potassium-channel blockers. The goal of this study was to determine whether the hyperpolarization is causally related to endothelium-dependent dilation of isolated cerebral arteries. ACh hyperpolarized rabbit middle cerebral arteries by up to 19 mV. The hyperpolarizations were sustained and did not occur in arteries without endothelial cells or in the presence of potassium-channel inhibitors (3 x 10(-6) M glibenclamide or 5 x 10(-5) M BaCl2). ACh-induced dilator responses were inhibited but not abolished by glibenclamide or BaCl2. Methylene blue also inhibited the dilator responses, and a combination of glibenclamide or BaCl2 and methylene blue greatly diminished the dilation. Nitric oxide relaxed but did not hyperpolarize the vascular smooth muscle cells, and BaCl2 had no effect on the nitric oxide-induced relaxations. These data indicate that the overall cerebral arterial dilator response to ACh is determined by the combined effects of membrane hyperpolarization, which closes voltage-dependent calcium channels, and the actions of a second endothelial factor, probably endothelium-derived relaxing factor.

Direct stimulation by succinate of Na+:K+ pump in rabbit ciliary epithelium

The effects of succinate on the intracellular potential difference, PDI, were measured in isolated rabbit ciliary processes. Concentration-dependent increases in the hyperpolarization of PDI occurred between 1 and 15 mM succinate in NaCl Ringers. With 5 mM succinate, there was a 6 mV hyperpolarization. Even though the hyperpolarization of PDI was comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PDI in either Cl(-)-free or HCO3(-)-free Ringers. Similarly, following incubation with either 0.1 mM DIDS or 3 mM BaCl2 the effect of succinate on PDI was unchanged. Five mM succinate had no effect if it was added after 5 mM malonate. Malonate (5 mM) rapidly reversed a 5 mM succinate-induced hyperpolarization of PDI which also suggests a metabolically mediated effect on PDI. An isosmotic substitution of Na+ with NMDG Ringers depolarized PDI, whereas PDI depolarized biphasically during exposure to 0.1 mM ouabain. The addition of 5 mM succinate had no effect on either the time course or the magnitude of the depolarization of PDI during blocking of the Na+:K+ pump with either Na(+)-free Ringers or ouabain. Taken together, these results show that succinate selectively stimulates the Na+:K+ pump, but has no effect on any Cl-, HCO3- or a Ba2(+)-sensitive K+ conductance.

Polarized 86Rb+ effluxes in primary cultures of rabbit kidney proximal cells: role of calcium and hypotonicity

Isolated proximal cells from rabbit kidney were seeded on collagen-coated permeable supports. After 8 days, the cultured cells became organized as a confluent monolayer. The proximal origin of the monolayer was confirmed by enzymatic, immunological, electrical and electron microscopical studies. The epithelia exhibited a morphological polarity that allowed for measurements of effluxes across the apical or the basolateral membranes. 86Rb was used as an isotopic tracer to indicate potassium movements. The 86Rb+ efflux across the basolateral face was 1.93-times that across the apical face, and both effluxes were pH dependent. Apical and basolateral 86Rb+ effluxes increased when the Ca2+ ionophore ionomycin (3 microM) was applied and when monolayers were exposed to a hypotonic medium. A pharmacological study revealed that BaCl2 (5 mM), tetraethylammonium (TEA, 20 mM) and Leiurus quinquestriatus hebraeus scorpion venom (from which charybdotoxin is extracted) abolished both ionomycin and hypotonically-stimulated effluxes, whereas apamin had no significant effect on the hypotonically-stimulated 86Rb+ efflux. This stimulated efflux was also abolished when monolayers were preincubated with pertussis toxin, but did not decrease in a Ca2(+)-free medium.

Analysis of biological samples using prompt gamma radiations induced by 14.7-MeV neutrons

We investigate a method for determining the elemental composition of biological samples that uses prompt gamma rays induced by 14.7-MeV neutrons. Alpha particles are produced simultaneously with the neutrons, which exit opposite the alpha detector through the vacuum chamber wall. The sample under investigation is irradiated and emits gamma radiations in a spectral energy distribution characteristic of the material. Barium-fluoride (BaF2) and high-purity germanium (HPGe) gamma detectors view the sample and record the spectrum of gamma radiation.

[Antiarrhythmic effect of Oenanthe javanica (Bl.) DC. injection]

The antiarrhythmic effect of Shuiqin (Oenanthe javanica) injection was studied in rats. An injection of 3 ml/kg iv could significantly antagonize the arrhythmias induced by aconitine and BaCl2, and decrease the rates of ventricular fibrillation and death induced by CaCl2. The results suggest that Shuqin injection has a significant antiarrhythmic effect on experimental rats.

[A comparison of anti-arrhythmic effects of four kinds of rhizoma seu radix Nomopterygii]

Experiments were conducted to compare the anti-arrhythmic effects of the four kinds of Qianghuo(Notopterygium incisum; N. forbesii; Pleurospermum rivulorum; Angelica silvestris). It has been found that all the four kinds of Qianghuo can antagonize arrhythmia induced by aconitine. Notopterygium incisum can prolong the ventricular vibration induced by CaCl2 and Pleurospermum rivulorum can prolong the ventricle stop induced by BaCl2. Thus Qianghuo can be used as a sedative and anti-arrhythmic drug.

Mechanisms underlying volume regulatory decrease by Necturus gallbladder epithelium

Volume regulatory decrease (VRD) by Necturus gallbladder epithelial cells in Cl Ringer was unaffected by the addition of 5 mM BaCl2 to apical perfusates but was inhibited by the addition of 5 mM BaCl2 and 50 or 3 microM phencyclidine (PCP) to serosal perfusates, suggesting that K channels in the basolateral membrane were activated during VRD. VRD was unaffected by replacement of Cl with NO3 or SCN, suggesting that Cl-dependent Na-K-Cl and K-Cl cotransport were not involved. In SCN Ringer, VRD was inhibited by the addition of 0.1 mM bumetanide to serosal perfusates, suggesting that bumetanide-sensitive anion channels in the basolateral membrane were also activated. A transient 10-mV hyperpolarization of the membrane potential was associated with VRD. The channel blockers that inhibited VRD had little or no effect on the hyperpolarization, suggesting that the changes in membrane potential were unrelated to the changes in cell volume. Perfusion of the apical surface of the epithelium with isotonic solutions containing 10 mM D-glucose resulted in a variable increase in cell volume followed by a variable shrinkage to normal, suggesting that VRD was also activated during organic solute absorption. The increase in cell volume was blocked by the addition of 0.01 or 1 mM phlorizin to mucosal perfusates. The reduction in cell volume was inhibited by the addition of 0.1 mM bumetanide, but not BaCl2 or PCP, to serosal perfusates, indicating the the shrinkage mechanism secondary to glucose addition differed from that seen after exposure to hypotonic perfusates.

[Anti-arrhythmic effects of matrine]

Matrine (MT) is an alkaloid isolated from Sophra alopecuroids L. The LD50 of MT iv to mice was 72.1 mg/kg (95% CL 68.2-76.5 mg/kg). MT had significant effects on different experimental models of arrhythmias induced by aconitine, barium chloride or coronary ligation. The ECG of anesthetized rats was significantly changed after iv of MT. The HR was retarded and the PR and QTc intervals were prolonged.

Inhibition of mucin secretion in a colonic adenocarcinoma cell line by DIDS and potassium channel blockers

The factors which influence the exocytosis of mucins are not well characterized. Since the physical properties of mucins may be affected significantly by the co-secretion of electrolytes and water, we studied the relationship between ion movement and mucin secretion in T84 cells, a human colonic adenocarcinoma cell line which has been well characterized with respect to apical chloride secretion. Secretion of mucin was assessed by immunoassay of mucin appearing in the medium within 30 min of stimulation. Cells were grown on plastic in DMEM/Ham's F12 medium and experiments were carried out at 70% confluence. Mucin secretion was stimulated by the calcium ionophore A23187, or A23187 plus vasoactive intestinal polypeptide. Stimulated mucin secretion was not affected by loop diuretics (furosemide (1 x 10(-3) M) or bumetanide (1 x 10(-4) M)), with or without the addition of ouabain (5 x 10(-5) M) and amiloride (1 x 10(-5) M), making it unlikely that transcellular chloride movements in necessary for mucin secretion. However, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; (1 x 10(-5) and 5 x 10(-5) M) and three potassium channel blockers BaCl2 (1 x 10(-3) and 5 x 10(-3) M), tetraethylammonium chloride (1 x 10(-2) M) and quinine (5 x 10(-4) M) inhibited mucin secretion. A DIDS-sensitive chloride channel or chloride/bicarbonate exchanger and a Ca2(+)-dependent potassium channel may play important roles in mucin secretion. Since plasma membranes are sparingly permeable to DIDS, the DIDS-sensitive site is likely to be on the apical plasma membrane, perhaps at an initiation locus for exocytosis.

Pharmacological modification of mechanical and electrical responses of frog heart to thrombin

The pharmacological modification of the thrombin effect on the mechanical and electrical responses of frog heart was examined in the Straub heart preparation and in single ventricular cells. Associated with the positive inotropic action thrombin increases voltage and duration of action potentials of isolated frog ventricular cells. As found by the patch-clamp technique in the cell-attached mode, thrombin stimulates single L-type Ca2+ channels, presumably mediated by a second messenger. The enhancement of contractility by thrombin depends on the proteolytic activity of the enzyme because enzymatically inactivated thrombin has no effect on frog hearts. The positive inotropic effect of thrombin as well as its stimulation of Ca2+ channel currents were inhibited by the protein kinase C blocker 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine (H7). However, phorbol 12-myristate 13-acetate (PMA), a known stimulator of protein kinase C, was ineffective in stimulating the inotropic action of thrombin. The inhibition of the thrombin-induced enhancement of contractility by indometacin indicates an involvement of arachidonic acid in the action of thrombin on frog heart.

Voltage-dependent calcium currents in trigeminal chick neurons

The presence of action potentials, when sodium and potassium currents were blocked, has been investigated in trigeminal ganglion neurons, using the patch-clamp technique. In this conditions, inward currents, sensitive to the external application of cadmium, were detected. Activation and inactivation properties were investigated, as well as the behaviour of the current in the presence of extracellular Barium. The properties of these inward currents in trigeminal neurons are correlated to high threshold voltage-dependent calcium channels.

Circulatory responses to vasoconstrictor agents during passive heating in the rat

The purpose of this study was to determine the actions of several pharmacological agents on the circulatory system, and more specifically on the superior mesenteric vascular bed, in response to environmental heat stress in chloralose-anesthetized rats. Animals were instrumented with Doppler flow probes on the mesenteric and renal arteries and exposed to an ambient temperature of 40 degrees C. Heart rate, mean arterial blood pressure (MAP), and core (Tc) and tail skin temperatures were also monitored. As Tc progressively increased from 37 degrees C during heat exposure, MAP rose to a plateau and then fell precipitously as Tc exceeded 41.5 degrees C. Mesenteric resistance increased throughout the early stages of heating before sharply declining prior to the reduction in MAP. The pressor and mesenteric resistance responses to constant infusions of several adrenergic agonists after MAP began falling (Tc = 41.3 degrees C) were significantly (P less than 0.05) attenuated compared with infusions into normothermic animals. In a second set of experiments, injections of both norepinephrine and angiotensin II were made 30 min before and approximately 10, 30, 50, 70, and 90 min after initiation of heating. These injections increased both MAP and mesenteric resistance; however, at TcS greater than 40 degrees C, the responses to both agonists were progressively and significantly attenuated. In a final group of animals, barium chloride infusions produced similar pressor and regional resistance changes during both normothermia and severe hyperthermia (Tc greater than 42 degrees C). These results indicate that, in the chloralose-anesthetized rat, hyperthermia disrupts adrenoceptor function but does not alter the intrinsic ability of vascular smooth muscle to contract.

[Anti-arrhythmic effects and electrophysiological properties of Ophiopogon total saponins]

The arrhythmias induced by chloroform-epinephine, BaCl2, and aconitine were prevented and antagonized by Ophiopogon total saponins (OTS) which were extracted from the root of Ophiopogon japonicus (Thunb) Ker-Gawl. The incidence of ventricular arrhythmia produced by ligation of the left anterior descending coronary artery was effectively decreased without any changes in the hemodynamic indices of dogs. The electrophysiological effects of OTS in vivo and in vitro were studied by means of contact electrode and intracellular microelectrode techniques. The results showed that OTS shortened APD10, APD50, APD90; decreased APA and Vmax of both monophasic and transmembrane action potentials. OTS also increased the ERP/APD ratio and prevented or abolished the arrhythmikinesis provoked by ouabain and aconitine. The anti-arrhythmic properties of OTS lead us to draw an inference that the anti-arrhythmic mechanism may be related to the blocking of sodium and calcium channels.

[Mutagen activity of barium chloride in Salmonella typhimurium]

Barium chloride, which is an important industrial chemical used in pigments, lacquers, dyes, glass and pesticide production, leather tanning and cloth dying, was tested on Salmonella typhimurium (TA 1535, TA 1537, TA 1538, TA 97, TA 98, TA 100) with the reverse mutation test, with and without metabolic activation, to assess its possible genotoxic effects and any possible action with respect to standard mutagens (sodium azide, 9-aminoacridine, 2-nitrofluorene, mitomycine-C, 2 aminoacridine). Using the platelet incorporation technique, barium chloride at various progressive concentrations gave negative results under the experimental conditions of the study.

Relaxant effects of alpha-adrenoceptor agonists in the rat isolated gastric fundus

In rat gastric fundus preparations with tone raised by the addition of barium chloride or carbachol, and in the presence of propranolol (2 microM) to prevent beta-adrenoceptor mediated effects, the adrenoceptor agonists noradrenaline, adrenaline, alpha-methylnoradrenaline, isoprenaline, cirazoline and phenylephrine all caused concentration-related relaxant responses. Relaxations to the catecholamines were poorly antagonized by prazosin (0.01-1 microM) resulting in the slopes of Schild plots being less than unity, low pA2 values for prazosin against the catecholamines and a clear relaxant effect of the catecholamines even in the presence of 1 microM prazosin. The prazosin-resistant relaxations were unaffected by higher concentrations of prazosin (2 microM) and propranolol (30 microM) or by further additions of idazoxan (1 microM) or haloperidol (30 microM). The relaxations were not due to a non-specific effect of the catechol nucleus since neither dihydroxyphenylethylene glycol (DOPEG) nor dihydroxyphenylacetic acid (DOPAC) produced relaxant effects at concentrations up to 300 microM. In contrast to the results with the catecholamines, prazosin was a potent antagonist of the relaxant effect of cirazoline and phenylephrine, although the antagonism was difficult to quantify due to a lowering of the slope of the concentration response curves to cirazoline and phenylephrine with the higher concentrations of prazosin (0.1 and 1.0 microM). In conclusion postjunctional relaxatory effects of catecholamines in the rat gastric fundus are mediated partly via alpha 1-adrenoceptors and partly via an atypical adrenoceptor.

Alteration in the sarcolemmal Na(+)-K+ pump of hindquarters resistance arteries in DOCA-salt rats

It has been suggested that a circulating inhibitor of the Na(+)-K+ pump contributes to the development and maintenance of DOCA-salt hypertension. However, the discordant results have been reported as to whether the sarcolemmal Na(+)-K+ pump in DOCA-salt hypertension is inhibited. Furthermore, no study has examined alteration in the sarcolemmal Na(+)-K+ pump of the true resistance arteries. We examined hindquarters vasoconstriction induced by ouabain (10(-3) M) in the vascularly isolated hindquarters of the DOCA-salt treated or control rats, which were perfused with Krebs-Henseleit solution. Hindquarters vasoconstriction induced by ouabain (10(-3) M) was greater in the prehypertensive and hypertensive DOCA-salt rats than in the corresponding control rats (p less than 0.01). We also examined hindquarters vasoconstriction induced by ouabain (10(-3) M) in the vascularly isolated hindquarters of the normal assay rats which were perfused by the plasma obtained from the DOCA-salt or control rats. The plasma of the prehypertensive and hypertensive DOCA-salt rats attenuated ouabain-induced hindquarters vasoconstriction in the assay rats (p less than 0.01). The plasma of the DOCA-salt rats did not alter nonspecific vasoconstriction caused by barium chloride. These results suggest that the plasma of the prehypertensive and hypertensive DOCA-salt rats had an inhibitor of the sarcolemmal Na(+)-K+ pump of the resistance arteries, but the sarcolemmal Na(+)-K+ pump molecules of the resistance arteries of those rats were increased. The in vivo activity of the sarcolemmal pump of the resistance arteries of the DOCA-salt rats would be determined by the relative influence of increased pump molecules and a circulating pump inhibitor.

Mechanically stripped pigmented and non-pigmented epithelium of the shark ciliary body: morphology and transepithelial electrical properties

Sections of intact ciliary epithelium and mechanically stripped non-pigmented (NPE) and pigmented (PE) cell layers of adult sharks (Squalus acanthias) were mounted in Ussing-type chambers (area 0.1 cm2). Addition of 10(-5) M forskolin to the aqueous side of intact epithelium significantly increased short-circuit current (Isc) within 15 min and a maximum of approx. 30 microA cm-2 was reached after 45-60 min. Transepithelial potential difference (V) increased from -0.8 mV (aqueous side negative as compared with blood/stromal side) to -1.5 mV, whereas resistance (R) was unchanged (50 omega cm2). Forskolin was without effect when applied to the blood side. In stripped PE preparations (R 15 omega cm2), 10(-5) M forskolin applied to the apical side induced a qualitatively similar change of Isc and V compared with the intact tissue. The forskolin-induced effects were fully reversed by 10(-4) M bumetanide and were not dependent on pretreatment of the tissue with 10(-3) M BaCl2. In stripped NPE preparations resistance was usually less than 10 omega cm2 and was not stable. This is consistent with the morphologic observation that although tight junctions were still demonstrable in stripped NPE cells, the apical membranes were damaged. In preparations taken for light and electron microscopy the stripped PE layer revealed intact epithelial cells. In particular, the basal thirds of the stripped PE cells were in very close contact with each other. These attachment zones may have the appearance of tight junctions. Thus the PE cells of the shark ciliary epithelium can be successfully isolated for transepithelial transport studies. The adenylate cyclase system is present in PE cells, and transepithelial transport of chloride may be regulated by intracellular cAMP.

Effects of ketamine on isolated human bronchial preparations

The bronchodilator effects of ketamine were examined in human bronchial preparations contracted maximally with histamine, acetylcholine, barium chloride or potassium chloride. Antagonism between ketamine and either histamine or acetylcholine was examined also. Ketamine caused bronchial relaxation irrespective of the constricting agent, and exerted a partial and non-competitive antagonism to histamine and acetylcholine. Propranolol and indomethacin did not inhibit the effect of ketamine, excluding the involvement of beta activation and of prostaglandins.