Glucose- and concentration-dependence of noradrenalin effects on electrical activity in mouse pancreatic beta cells

The effects of a wide range of noradrenalin (NA) concentrations (10(-11)-10(-4) M) on the membrane potential and on the glucose-induced electrical activity were investigated with microelectrodes in microdissected mouse islets. In the presence of 11.1 mM glucose, the beta cells exhibited a repetitive activity. NA at more than 10(-7) M induced a rapid hyperpolarization followed by a silent depolarization, then by the appearance of a slowed pace of repetitive activity (dose-dependent effects). NA at less than 10(-7) M did not markedly affect the electrical activity; it only induced a dose-dependent increase in the degree of activity with no change of the potential levels. The glucose-dependence of these effects were then investigated. In the absence of glucose, 10(-8) and 10(-6) M NA did not affect the resting membrane potential. Non-stimulatory glucose concentrations (2.8-7.3 mM) progressively decreased the membrane potential. 10(-8) M NA did not affect it, while 10(-6) M NA induced a dose-dependent and long-lasting hyperpolarization. In the presence of stimulatory glucose concentrations (7.3-30 mM) the degree of activity increased, 10(-8) M NA induced a slight leftward shift and 10(-6) M NA a slight rightward shift of the dose-response curve.     

Effects of spantide on guinea pig coronary resistance vessels.

Effects of spantide ([D-Arg1,D-Trp7,9,Leu11]substance P) on coronary resistance vessels were studied in isolated guinea pig hearts perfused at constant rate with isotonic buffer containing 20 or 40 mM KCl. Spantide (1 microM) caused a 20-fold rightward shift of the substance P (SP) dose-response curve for vasodilation with no change in maximum (KB = 5.3 x 10(-8) M). Bolus injections of 0.25 to 250 pmol spantide had no effect, but higher doses caused a brief vasodilation followed by a larger, more prolonged vasoconstriction. Histamine produced similar changes in perfusion pressure. Antihistamines (H1 and H2) reduced or blocked responses to spantide and histamine. These findings indicate spantide is a competitive antagonist to SP in guinea pig coronary resistance vessels. In addition, high doses of spantide can cause prominent vascular effects which are mediated by histamine.     

Sodium nitroprusside relaxes goat coronary artery through activation of calcium-dependent K+ channels

In the present investigation we have examined the hypothesis that calcium-dependent K+ channels (K(Ca)) are involved in the sodium nitroprusside (SNP)-induced vasodilatation of goat coronary artery. SNP (10(-9)-3 x 10(-6) M), added cumulatively, relaxed K+ (30 mM)-contracted coronary artery ring segments in a concentration-dependent manner with an EC50 of 1.32 x 10(-7) M (95% CL, 0.93-1.86 x 10(-7) M; n = 21). K(Ca) blocker, tetraethyl ammonium (1 mM) caused a rightward shift in the concentration-response curve of SNP with a corresponding increase in EC50 (1.62 x 10(-6) M; 95% CL, 0.44-6.02 x 10(-6) M, n = 4) of nitro vasodilator. Lowering of extra cellular Ca2+ in the physiological saline solution to 1/4 of normal selectively attenuated the vasorelaxant response of SNP, thereby causing an increase in its EC50 (2.4 x 10(-6) M; 95% CL, 1.23-4.68 x 10(-6) M, n = 4). Exposure of the tissues to high K+ (80 mM) solution, a protocol adopted to reduce the K+ gradient across the cell membrane, markedly inhibited the coronary artery relaxations induced by SNP (EC50, 2.54 x 10(-6) M; 95% CL, 1.31-4.91 x 10(-6) M, n = 4), when compared with tissues contracted with low K+ (30 mM) solution (EC50 7.9 x 10(-8); 95% CL, 4.4 x 10(-8)-1.44 x 10(-7) M, n = 6). The results suggested that a major component of SNP-induced relaxation of goat coronary artery was mediated by K(Ca) channels.     

Interactions between endothelin and atrial natriuretic factor in the rat aortic ring preparation.

The potential interaction (s) between atrial natriuretic factor (ANF) and porcine--human endothelin (ET-1) was investigated in the endothelium-denuded rat aortic ring preparation. ET-1 produced a sustained contraction of aortic rings with an ED50 of 3.6 +/- 0.49 x 10(-9) M. Within the concentration range of 10(-9) to 10(-7) M, both rat ANF 103-126 and rat ANF 99-126 when preincubated with tissues reduced the contractile efficacy of ET-1 especially at low concentrations resulting in a small but significant rightward shift of the dose--response curve to ET-1. In contrast, at a concentration of 10(-10) M, rANF 99-126 but not rANF 103-126 produced a significant leftward shift of the dose--response curve to ET-1 and an increase in the maximal developed tension for the dose--response curve to ET-1. For tissues incubated in the absence of extracellular calcium or in the presence of the calcium channel blocker nifedipine (5 x 10(-7) M), both ANF derivatives produced a dose-dependent decrease in the maximum contraction, but no change in potency to ET-1. Addition of either rANF 103-126 or rANF 99-126 to tissues maximally contracted with ET-1 resulted in relaxation, reaching a maximum of 70%. The ED50 values for relaxation were 2.7 +/- 0.51 x 10(-8) and 3.5 +/- 0.60 +/- 10(-8) M for rANF 103-126 and rANF 99-126, respectively. ET-1 did not interact with biologically responsive and clearance receptors for ANF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Benzilylcholine mustard and spare receptors in guinea pig ileum

A comparison was made of muscarinic receptor occupancy by the irreversible antagonist benzilylcholine mustard (BCM) as determined from shifts in the dose-response curve to a muscarinic agonist and from 3H-QNB binding to homogenates of BCM-treated tissue. Major discrepancies were found. A low concentration of BCM (3x10-8M/15 min.) produced a parallel dose-response curve shift corresponding to 98-99% receptor occupancy by BCM, whereas 3H-QNB binding revealed only 48% receptor occupancy. Possible origins of this discrepancy are discussed. High concentrations of BCM (5x10-5M, 15 min.) fail to completely alkylate all 3H-QNB binding sites even though response is completely lost. Although significant (64%) recovery of response occurs after prolonged tissue washing (240 min.) this is not accompanied by an increase in 3H-QNB binding. The small fraction (approximately 5%) of sites inaccessible to BCM and with reduced affinity for 3H-QNB may represent a subpopulation of muscarinic receptors.     

Positive inotropic effect of ethylephrine on the isolated rat atria

Ethylephrine, a sympathomimetic amine which belongs to the phenolamine group, was assayed on the driven left rat atrium. The frequency response curve was performed for norepinephrine and ethylephrine. The maxima was attained for both compounds at 1 Hz. The agonist under study has an inotropic action less potent than the classical catecholamines. Propranolol (10(-8) and 10(-7) M) produced a parallel shift to the right in the log dose-response curves of ethylephrine with no decrease in the maximal response, indicating that the antagonism was competitive. In the presence of cocaine or with reserpine-pretreatment the sensitivity of the preparation to the amine did not vary. The alpha-blocker, phentolamine (10(-8) to 3.10(-5) M) did not possess an inotropic effect per se. In contrast, phentolamine, delivered to the bath beforehand, did not block the agonist. However at 10(-8) and 10(-7) M increase the maximal response both in normal and reserpinized preparations. It is suggested that ethylephrine is a direct inotropic preparation. It is suggested that ethylephrine is a direct inotropic agent on the driven left rat atrium and its effects are mediated by beta-receptors. The results also indicate the lack of evidence that ethylephrine has any action on the alpha-receptors.     

Effect of KATP channel openers on myogenic and neurogenic responses in goat urinary bladder

Isolated goat detrusor muscle exhibited spontaneous contractility with an irregular amplitude and frequency. The spontaneity of detrusor muscle exhibited a mean amplitude as 11.99 +/- 0.83 mm and frequency as 1.37 +/- 0.16/min. KATP-channel openers namely, cromakalim or pinacidil (10(-7) - 10(-4) M) added cumulatively, elicited a concentration-related inhibition of both amplitude and rate of spontaneous contractions. The mean IC50 values for both amplitude and frequency for cromakalim were 3.3 x 10(-6) M and 2.9 x 10(-6) M, respectively; and for pinacidil were 2.0 x 10(-5) M and 1.5 x 10(-5) M, respectively. Glibenclamide, a KATP-channel blocker inhibited the cromakalim-induced concentration-related relaxation of spontaneous contractions with a significant increase in its mean IC50. ACh-induced concentration-related contractile response was inhibited in the presence of either cromakalim (10(-4) M) or pinacidil (10(-4) M). The mean EC50 value of ACh, in the presence of cromakalim (2.5 x 10(-3) M) was significantly increased as compared to the control (1.2 x 10(-6) M). In the presence of glibenclamide (10(-5) M) the inhibitory effect of cromakalim was significantly reduced with consequent decrease in the EC50 value (1.9 x 10(-5) M). Application of EFS (30 V and 5 ms) on goat urinary bladder strips at 1, 2, 5, 10, 20 and 30 Hz elicited frequency-related contractile responses. Both cromakalim and pinacidil caused a rightward shift in the frequency-related contractile response curve with significant increase in the mean EF25 and EF50 values, respectively. In the presence of glibenclamide (10(-4) M), the frequency-related inhibitory response curve was shifted to left with significant (P < 0.001) increase in the mean EF25, EF50 and EF75. The present results suggest that in the goat detrusor muscle, agonist and EFS-induced contractile responses were more potently inhibited by cromakalim than pinacidil with activation of glibenclamide sensitive KATP channels.     

Intact human lymphocyte membranes respond to muscarinic receptor stimulation by oxotremorine with marked changes in microviscosity and an increase in cyclic GMP

The muscarinic agonist oxotremorine produced a linear dose-dependent increase in membrane fluidity of intact and viable human lymphocytes in vitro. This effect proved to be receptor-mediated because preincubation with 10(-5)M atropine shifted the dose-response curve one order of magnitude rightward. Pirenzepine preincubation did not affect membrane fluidity variation. A cGMP increase was also found after oxotremorine treatment. The results are discussed in terms of possible modulation of guanyl cyclase and adenyl cyclase through membrane fluidity variations.     

A synthetic peptide derivative that is a cholecystokinin receptor antagonist

So far, there are no known peptidic effective receptor antagonists of both peripheral and central effects of cholecystokinin (CCK). Here, we describe a synthetic peptide derivative of CCK, t-butyloxycarbonyl-Tyr(SO3-)-Met-Gly-D-Trp-Nle-Asp 2-phenylethyl ester 1 (where Nle is norleucine), which is a potent CCK receptor antagonist. In rat and guinea pig dispersed pancreatic acini, this peptide derivative did not alter amylase secretion, but was able to antagonize the stimulation caused by cholecystokinin-related agonists. It caused a parallel rightward shift in the dose-response curve for the stimulation of amylase secretion with half-maximal inhibition of CCK-8-stimulated amylase release at a concentration of about 0.1 microM. Compound 1 was able to inhibit the binding of labeled CCK-9 (the C-terminal nonapeptide of CCK) to rat and guinea pig pancreatic acini (IC50 = 5 X 10(-8) M) as well as to guinea pig cerebral cortical membranes (IC50 = 5 X 10(-7) M). These results indicate that Compound 1 is a potent competitive CCK receptor antagonist.     

Dactinomycin is a competitive neurokinin-2 receptor antagonist.

Dactinomycin, a peptide antibiotic from Streptomyces spp., is a classical agent which inhibits DNA replication. In the present study, dactinomycin inhibited specific [125I]NKA binding in rat colon membranes (KI = 1.05 x 10(-5) M) in a competitive manner. Furthermore, dactinomycin caused a parallel rightward shift of the concentration-response curve for the contractions in the rat colon induced by the NK-2 receptor agonist [Nle10]-NKA(4-10). A selective inhibition of NK-2 receptors by dactinomycin was supported by the absence of inhibition of NK-1 receptors activation in guinea pig vas deferens and of NK-3 receptors in rat portal vein. The structural similarity of the cyclic peptide moieties of dactinomycin to L-659,877, a known NK-2 receptor antagonist, can probably account for the present observations.     

Calcium dependence of the contractile response of the aorta in the rat, rabbit and guinea pig and in the human uterine artery

The influence of extracellular Ca2+ on the contraction produced by noradrenaline (NA) (3 x 10(-6) M), KCl (60 mM) and BaCl2 (30 mM) on human uterine arteries (AUH) and aortic strips from rats, rabbits and guinea-pigs have been studied. The vessels were cut spirally and incubated in Krebs solution containing 2.5 mM Ca2+ (KN), 0 mM Ca2+ (K-0Ca) or 0 mM Ca2+ + 3 mM EDTA (K-EDTA). Both phases (fast and slow) of the response of aortic strips to NA and of the AUH to NA, KCl and BaCl2 were significantly smaller in solutions without Ca2+. Only in rabbit aortic strips the slow phase was significantly more reduced than the fast phase. Overall, the contractions of the rat aortic strips were most resistant to the absence of extracellular Ca2+. These results confirm the variability of the responses of blood vessels from different vascular beds and species to the removal of extracellular Ca2+.     

The facilitative actions of Bay K 8644 on norepinephrine and KCl-induced contractures of rabbit aortic rings

The effect of the calcium channel agonist BAY K 8644 on the ability of KCl and norepinephrine to induce contractions of rabbit aortic rings has been examined in Krebs-Henseleit buffer containing either 4.0 or 6.8 mM potassium. BAY K 8644 (10(-8) to 10(-6) M) alone induced slowly developing aortic contractures which were 10 (at 4.0 mM potassium) or 20 (at 6.8 mM potassium) percent of the maximum obtainable with norepinephrine. These contractions were not observed in every experiment, but were more likely to occur at 6.8 mM (71% at 10(-6) M BAY K 8644) when compared to 4.0 mM (31% at 10(-6) M BAY K 8644) potassium buffer. BAY K 8644, in either potassium buffer, induced a statistically significant shift to the left in the norepinephrine dose-response curve. The norepinephrine dose-response curve was significantly curvilinear in the presence of 3 X 10(-8) M BAY K 8644 (6.8 mM potassium) and 10(-6) M BAY K 8644 (4.0 mM potassium). Similarly, BAY K 8644 induced sinistral shifts in the KCl dose-response curve with a curvilinear function observed at 3 X 10(-7) M BAY K 8644. These data show that BAY K 8644 is capable of inducing aortic contractures at potassium concentrations significantly lower than previously reported. Furthermore, BAY K 8644 facilitates opening of calcium channels by either potassium or norepinephrine. In contrast to others, our data indicates that BAY K 8644 can affect calcium channels activated by norepinephrine. Finally, our data suggest that the alpha and dihydropyridine receptors are capable of interacting and that occupation of one receptor can affect the action of a compound binding to the other receptor.     

Sodium arsenite and cadmium chloride induction of proteasomal inhibition and HSP accumulation in Xenopus laevis A6 kidney epithelial cells

Sodium arsenite (NA) and cadmium chloride (CdCl(2)) are relatively abundant environmental toxicants that have multiple toxic effects including carcinogenesis, dysfunction of gene regulation and DNA and protein damage. In the present study, treatment of Xenopus laevis A6 kidney epithelial cells with concentrations of NA (20-30 μM) or CdCl(2) (100-200 μM) that induced HSP30 and HSP70 accumulation also produced an increase in the relative levels of ubiquitinated protein. Actin protein levels were unchanged in these experiments. In time course experiments, the levels of ubiquitinated protein and HSPs increased over a 24h exposure to NA or CdCl(2). Furthermore, treatment of cells with NA or CdCl(2) reduced the relative levels of proteasome chymotrypsin (CT)-like activity compared to control. Interestingly, pretreatment of cells with the HSP accumulation inhibitor, KNK437, prior to NA or CdCl(2) exposure decreased the relative levels of ubiquitinated protein as well as HSP30 and HSP70. A similar finding was made with ubiquitinated protein induced by proteasomal inhibitors, MG132 and celastrol, known to induce HSP accumulation in A6 cells. However, the NA- or CdCl(2)-induced decrease in proteasome CT-like activity was not altered by KNK437 pretreatment. This study has shown for the first time in poikilothermic vertebrates that NA and CdCl(2) can inhibit proteasomal activity and that there is a possible association between HSP accumulation and the mechanism of protein ubiquitination.     

Leukotriene and anti-IgE induced contractions of human isolated trachea: studies with leukotriene receptor antagonists and a novel 5-lipoxygenase inhibitor

The pharmacological actions of three leukotriene D4 (LTD4) receptor antagonists, FPL-55712, L-648,051, and L-649,923, and a novel inhibitor of leukotriene biosynthesis, L-651,896, have been investigated on isolated human tracheal smooth muscle. In the order of potency L-648,051 greater than FPL-55712 greater than L-649,923, these agents antagonized contractions to LTD4 and produced parallel rightward shifts in the dose-response curves. Mean -log KB values against LTD4 were 6.9 +/- 0.1, 6.5 +/- 0.3, and 6.0 +/- 0.1 for L-648,051, FPL-55712, and L-649,923, respectively. FPL-55712 also antagonized contractions to LTC4 (-log KB value, 6.4 +/- 0.3) and this activity was not decreased by the gamma-glutamyl transpeptidase inhibitor, L-serine borate. In the presence of 1 x 10(-7) M atropine, 7 x 10(-6) M mepyramine, and 1.4 x 10(-6) M indomethacin, L-648,051 at 2 x 10(-5) and 2 x 10(-6) M produced complete and partial blockade, respectively, of the contraction to goat anti-IgE. L-649,923 and FPL-55712 produced partial but significant inhibition at 2 x 10(-5) M, whereas the 5-lipoxygenase inhibitor, L-651,896, produced almost complete inhibition at 3.5 and 35 x 10(-6) M. L-Serine borate (15 mM) did not alter the the activity of FPL-55712 versus anti-IgE. These findings indicate that LTD4 receptors mediate contraction of human trachea to exogenously applied and endogenously (anti-IgE) released leukotrienes. LTD4 antagonists, such as L-648,051, may be useful in assessing the role of leukotrienes in respiratory disease.     

Innervation of human omental arteries and veins and vasomotor response to noradrenaline, neuropeptide Y, substance P and vasoactive intestinal peptide

Human omental arteries and veins are supplied with nerve fibers containing noradrenaline (NA) and neuropeptide Y (NPY); these two agents probably co-exist in perivascular sympathetic nerve fibers. Substance P (SP)- or vasoactive intestinal peptide (VIP)-containing fibers could not be detected. In studies on isolated omental vessels NA produced constriction. The results of blockade experiments suggest that human omental arteries are equipped predominantly with alpha 1-adrenoceptors and omental veins with a mixture of alpha 1- and alpha 2-adrenoceptors. NPY at a concentration of 10(-7) M or higher had a weak contractile effect on veins and virtually no effect on arteries. NPY at a concentration of 3 X 10(-8) M shifted the NA concentration response curve to the left in arteries (pD2 = 5.8 for NA versus 6.6. for NA in the presence of NPY; P less than 0.001) but not in veins. Both SP and VIP relaxed arteries precontracted with NA or prostaglandin F2 alpha (PGF2 alpha). The potency of SP as a relaxant agent was similar in arteries and veins; the effect of VIP was elicited at lower concentrations in veins than in arteries.     

含氯化镉水体中螺旋藻的生长及其对镉的摄取作用

研究了钝顶螺旋藻和极大螺旋藻在含CdCl2水体中的生长状况与摄Cd能力.结果表明:两种螺旋藻皆对CdCl2有较强的耐受能力,但是有不同的摄Cd行为.当CdCl2浓度为6~24mg.L-1,培养96h时,两种螺旋藻对Cd的摄取作用主要表现为藻细胞外的表面吸附;培养10d时,钝顶螺旋藻的胞内Cd含量依然甚微,而极大螺旋藻对Cd的细胞内吸附量却明显增加,24mg.L-1CdCl2处理的极大螺旋藻胞内的Cd吸附量为12mg.L-1CdCl2处理的11.6倍,且略超过细胞表面吸附量.表明在高浓度Cd的长时间胁迫下,两种螺旋藻的摄Cd行为和对Cd的耐受机制具有明显差异,其中钝顶螺旋藻为胞外机制,而极大螺旋藻却为胞内、胞外混合机制,且以胞内机制为主.     

Microwave Facilitation of Methylnaltrexone Antagonism of Morphine-Induced Analgesia in Mice

Exposure to low dose microwave irradiation has been postulated to influence effects of centrally active pharmacological agents. In this investigation, the analgesic dose, 50% (ADSO) for morphine in the mouse tail flick test was significantly increased by pretreatment with the centrally active opiate receptor blocker naltrexone, and the dose-response curve ms shifted significantly to the right. On the other hand, the AD50 and dose-response curve for morphine were not influenced by either the peripherally active opiate receptor blocker methylnaltrexone alone or microwave irradiation (2.45 GHz, 20 mW/cm², CW, 10 min) alone. However, following both methylnaltrexone pretreatment and microwave exposure, there was both a significant increase in the AD50 as well as a significant rightward shift of the dose-response curve, indicating a competitive antagonism of morphine by methylnaltrexone. One possible explanation for this microwave-drug interaction is that microwave energy might facilitate entry of methylnaltrexone into the central nervous system.     

Genotoxic effects and induction of phytochelatins in the presence of cadmium in Vicia faba roots

This study investigates different effects in roots of Vicia faba (broad bean) after exposure to cadmium. Genotoxic effects were assessed by use of the well-known Vicia root tip micronucleus assay. Cytotoxic effects were evaluated by determining the mitotic index in root tip cells. Finally, molecular induction mechanisms were evaluated by measuring phytochelatins with HPLC. After hydroponical exposure of V. faba roots to a range of cadmium concentrations and during different exposure times, the results of this approach showed large variations, according to the endpoint measured: after 48 h of exposure, genotoxic effects were found between 7.5 x 10(-8) and 5 x 10(-7)M CdCl(2), and cytotoxic effects were observed between 2.5 x 10(-7) and 5 x 10(-7)M CdCl(2). Statistically significant phytochelatin (PC) concentrations were measured at >or=10(-6)M CdCl(2) for PC(2), and at >or=10(-5)M CdCl(2) for PC3 and PC4.     

Role of calcium in the potentiating effect of phorbol ester on KCl-induced vasocontraction

The mechanism of the potentiating effect of phorbol ester on potassium-induced contraction in rat aorta was investigated. The contractile response to KCl in the medium containing 0.5 mM CaCl2 was significantly increased by pretreatment with 10(-8) M phorbol 12-myristate 13-acetate (PMA), but not with 10(-7) M 4 alpha-phorbol. The dose-response curve to calcium in 30 mM KCl-induced contraction was shifted to the left by PMA pretreatment and the EC50 value (the concentration producing a half maximal response) of calcium was significantly lower in aorta pretreated with PMA than in the control. On the other hand, calcium influx stimulated by 30 mM KCl was not changed by PMA pretreatment. Both the contractile response and the corresponding calcium influx induced by 30 mM KCl were abolished by preincubation with 10(-6) M verapamil for 45 min. These results suggest that activation of protein kinase C potentiates the contractile response to KCl by increasing the sensitivity of the intracellular contractile apparatus for calcium.     

HbO2 dissociation in man during prolonged work in chronic hypoxia.

In healthy human sojourners to 3,100 m we studied exercise-induced shifts in HbO2 dissociation: their regulation in femoral venous blood and their net effect on estimated capillary PO2 (PC-O2) in working skeletal muscle. Prolonged heavy work effected an increase of 10.3 plus or minus 0.9 mmHg in in vivo P50 (7.30 PH-v, 41 degrees C-v, and 45 Pv-CO2); due entirely to the additive effects of increased venous temperature and [H+]. The rightward curve shift during work at 3,000 m, compared to that at 250 m, produced a similar increase in in vivo P50 but a reduced net effect on PC-O2, because Cv-02 at 3,100 m was reduced similar to 2 ml/100 ml to the lower converging portions of the curve. The lower Cv-O2 (and Pv-O2) at 3,100 M was attributable to a small decrease in total systemic blood flow. The net effect of the rightward curve shift during exercise on mean to end-capillary PO2 was positive in most cases (+1 to +8 mmHg PCO2). However, it was shown that the levels of mean to end-capillary PO2 (28-13 mmHg), which would have been obtained during exercise in the absence of any rightward curve shift, were more than adequate to sustain a steady state of aerobic energy production in working skeletal muscle. These data do not support the concept of a significant contribution to oxygen delivery to working skeletal muscle from in vivo shifts in HbO2 dissociation, during either acclimatization to high altitude or during prolonged muscular work.