Search results for "Guinea Pig"
showing 10 items of 372 documents
Characterization of adenosine receptors in guinea-pig isolated left atria
1989
1. The effects of purinergic stimulation on action potential, force of contraction, 86Rb efflux and 45Ca uptake were investigated in guinea-pig left atria. 2. Adenosine exerted a negative inotropic effect which was antagonized by adenosine deaminase but enhanced by dipyridamole. 3. The negative inotropic effect of adenosine was mimicked by 5'-(N-ethyl)-carboxamido-adenosine (NECA) and the isomers of N6-(phenyl-isopropyl)-adenosine, R-PIA and S-PIA. NECA and R-PIA were about 100 times more potent than adenosine, whereas R-PIA was about 100 times more potent than S-PIA. 4. The inotropic effects of adenosine (in the presence of dipyridamole), NECA, R-PIA and S-PIA were competitively antagonize…
Adrenoceptor-mediated effects on calcium channel currents are antagonized by 5?-(N-ethyl)-carboxamido-adenosine in guinea-pig atrial cells
1992
In guinea-pig atrial myocytes, the effects of the adenosine analogue 5′-(N-ethyl)-carboxamido-adenosine (NECA) in the presence of isoprenaline (ISO) on Ca2+ channel activity were analyzed. Single Ca2+ channel currents were recorded from cell-attached patches by application of several hundred 100 ms depolarizing steps. Under control conditions, burstlike activity of channel openings during some depolarizing steps were followed by variably long periods of quiescence (blank sweeps). During superfusion with ISO (100 nmol/l), ensemble-averaged (mean) current was increased by about 150%. The underlying mechanism was found to be a significant increase in the channel availability, defined as the ra…
Tachykinin-, calcitonin gene-related peptide-, and protein gene product 9.5-immunoreactive nerve fibers in alveolar walls of mammals.
1991
The presence and distribution of the presumed pan-neural marker protein gene product 9.5 (PGP)- and peptide-immunoreactive (ir) nerve fibers in alveolar walls of various species was investigated by light microscopic single and double staining immunohistochemistry. PGP-, tachykinin (TK)-, and calcitonin gene-related peptide (CRGP)-ir fibers were sparsely distributed in a similar pattern in alveolar walls of all species investigated. No vasoactive intestinal peptide-, peptide histidine isoleucine-, galanin-, and opioid-ir nerve fibers could be detected. PGP-ir fibers outnumbered those staining for TKs and CGRP. There was partial coexistence of PGP and TK as well as of TK and CRGP. PGP-, TK-, …
Analysis of the hyperpolarizing effects of forskolin in guinea-pig atrial heart muscle.
1988
The effects of forskolin on action potential configuration and on both uptake and efflux of 86Rb+ were studied in guinea-pig left atria. The action potential was prolonged by forskolin in the plateau range but shortened at the end of repolarization; maximal upstroke velocity and amplitude of slow response potentials were enhanced. In partially depolarized preparations, the resting potential was increased by forskolin; this effect was not prevented by atropine 1 μmol/1. Forskolin augmented the rate constant of 86Rb+ efflux in beating and in resting preparations. The uptake of 86Rbs+ was enhanced by forskolin in resting preparations. It is concluded that forskolin stimulates the Na+, K+ -pump…
Pre- and postsynaptic effects of muscarinic agonists in the guinea-pig ileum
1980
The effects of several muscarinic agonists on smooth muscle (postsynaptic effect) and on acetylcholine release (presynaptic effect) were compared in the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum. 1. For release experiments the acetylcholine stores of the preparation were labelled with 3H-choline. Electrical field stimulation in the absence of a cholinesterase inhibitor caused an outflow of tritium that reflected release of 3H-acetylcholine. The agonists oxotremorine, arecaidinepropargylester, methylfurmethide, muscarine, carbachol, arecoline and pilocarpine inhibited the stimulation-induced outflow in a concentration-dependent manner. At the highest concentrat…
The release of choline from phospholipids mediated by beta-adrenoceptor activation in isolated hearts.
1986
The resting efflux of choline into the perfusate (Tyrode's solution) of isolated hearts was equal to the rate, at which choline was liberated from phospholipid degradation (Lindmar et al. 1986). Infusion of isoprenaline (2 X 10(-7) mol/l), forskolin (1-3 X 10(-6) mol/l) or 3-isobutyl-1-methylxanthine (IBMX; 3 X 10(-4) mol/l) for 40 min markedly enhanced the efflux of choline. The increase was linear during the experimental period and, in the case of isoprenaline, was blocked by 3 X 10(-7) mol/l atenolol. In the guinea-pig heart, IBMX at a threshold concentration of 10(-4) mol/l shifted the concentration-response curve for the effect of forskolin on the efflux of choline to the left by one l…
Pharmacological investigation into the effects of histamine and histamine analogues on guinea-pig and rat colon in vitro.
1986
The effects of histamine and specific histamine agonists has been examined on isolated longitudinal colon strips of guinea-pig and rat. Histamine and 2-pyridyl-ethylamine but not 4 methylhistamine produced a concentration-related contractile response in the guinea-pig colon. The H1-antagonist clemizole antagonized competitively the effect of histamine but the H2-antagonist ranitidine did not modify the dose-response curve to histamine in the guinea-pig colon. Atropine, hexamethonium, prazosin and propranolol failed to modify the contractile response to histamine. Tone induced with KCl in guinea-pig isolated colon was not modified by histamine agonists even in tissues pretreated with clemizo…
Adenosine activates a potassium conductance in guinea-pig atrial heart muscle.
1983
Adenosine shortens the action potential and diminishes the force of contraction in guinea-pig left atria. These effects may be brought about by the activation of a potassium conductance. This assumption is supported by voltage clamp and 42K release experiments.
Relaxation by Calcium Antagonists of Potassium-contracted Trachea from Normal and Sensitized Guinea-pigs: Influence of Epithelium and the Surface of …
1993
Abstract A technique by which drug access was restricted to either the mucosal or the adventitial surface of tracheal rings, isolated from normal (unsensitized) or sensitized guinea-pigs, was used to study the role of the epithelium in the relaxation produced by calcium antagonists (verapamil, nifedipine, cinnarizine and flunarizine) of K+-induced contraction. In trachea from normal guinea-pigs, the relaxation to verapamil for unrestricted or mucosal drug entry was reduced in the absence of epithelium, whereas the relaxation produced by nifedipine, cinnarizine or flunarizine was unchanged. In sensitized trachea, the relaxation elicited by the calcium antagonists tested was similar in intact…
Failure of opioids to affect excitation and contraction in isolated ventricular heart muscle
1989
The opioid agonists morphine (selective for mu-receptors) and ethylketocyclazocine (selective for kappa-receptors), at concentrations evoking strong effects in neuronal structures, did not significantly affect the configuration of the intracellularly recorded action potential and the force of contraction in ventricular heart muscle isolated from guinea pigs, rabbits and man. These results suggest that any changes of heart functions in vivo in response to opioid-like drugs are probably not mediated postsynaptically at the myocardial cell membrane but rather presynaptically, influencing the release of noradrenaline and/or acetylcholine from the nerve terminals.