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  • 1
    Electronic Resource
    Electronic Resource
    Acetylcholine and adenosine activate the G protein-gated muscarinic K+ channel in ferret ventricular myocytes (1995)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 351 (1995), S. 610-617 
    Details
    ISSN: 1432-1912
    Keywords: Ferret ; Ventricular myocytes ; Acetylcholine ; Adenosine ; Muscarinic K+ ; channel ; G protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The properties of the K+ channel activated by acetylcholine (ACh) and adenosine (Ado) were examined in single ferret ventricular myocytes using patch-clamp techniques. In the whole-cell configuration, ACh and Ado induced an inwardly rectifying K+ current and shortened the action potential duration. The effect of ACh was blocked by atropine, while the Ado effect was interrupted by 8-cyclopenty1,1,2-dipropyl xanthine, a specific Ado A1 receptor antagonist. In cell-attached recordings, ACh and Ado added to the pipette solution activated a single population of inwardly rectifying K+ channels, distinct from the i K1 channel. The channel had a slope conductance of ∼ 40 pS in symmetrical 150 mM K+ solutions and a mean open time of 0.8 ms. Excision of the patch into the inside-out patch configuration in guanosine triphosphate (GTP)-free solution abolished the channel activity. The channel was reversibly reactivated by adding GTP to the intracellular side of the patch. GTPγS activated the channel irreversibly. When the inside-out patch was treated with the A protomer of pertussis toxin (PTX), intracellular GTP no longer activated the K+ channel. The results show that ferret ventricular myocytes possess a K+ channel activated by both muscarinic and Ado A1 receptors. Its electrophysiological properties and the gating by a PTX-sensitive G protein in a membrane-delimited fashion are identical with those of the muscarinic K+ channels in nodal and atrial tissues of other species. In conclusion, the G protein-gated muscarinic K+ channel is expressed in ferret ventricular myocardium and may underlie the direct negative inotropism of ACh and Ado in this tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170160
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Pronounced direct inhibitory action mediated by adenosine A1 receptor and pertussis toxin-sensitive G protein on the ferret ventricular contraction (1993)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 348 (1993), S. 282-289 
    Details
    ISSN: 1432-1912
    Keywords: Adenosine ; Phenylisopropyladenosine ; Adenosine receptors ; Negative inotropic effect ; G proteins ; Ferret ventricular myocardium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An adenosine A1 receptor agonist R-N6-phenylisopropyladenosine (R-PIA) elicited a pronounced negative inotropic effect with the EC50 value of 0.69 μmol/1 in the presence of a β-adrenoceptor blocking agent bupranolol (0.3 μmol/1) in the isolated ferret papillary muscle. The negative inotropic effect of R-PIA was not associated with changes in cyclic AMP level. Adenosine and other A1 receptor agonists also elicited a negative inotropic effect. DPCPX (1,3-dipropyl-8-cyclopentyl xanthine) antagonized the negative inotropic effect of R-PIA in a competitive manner (pA2 value = 8.4). The inhibitory action of R-PIA was markedly attenuated in the ventricular muscle preparation isolated from ferrets pretreated with pertussis toxin that caused ADP-ribosylation of 39 kDa proteins in the membrane fraction. In the membrane fraction derived from the ferret ventricle, [3H]-DPCPX bound to a single binding site in a saturable and reversible manner with high affinity (Kd value = 1.21±0.41 nmol/l; B max = 12.8±3.02 fmol/mg protein; n = 7). The binding characteristics of [3H]-DPCPX in the rat ventricle (Kd value = 1.51 ±0.09 nmol/l; B max = 12.7±1.47 fmol/mg protein; n = 5) were similar to those in the ferret. On the other hand, the content of Go, a major pertussis toxin-sensitive G protein in the ferret heart, was much higher in the ferret than in the rat ventricle. The present results indicate that adenosine receptors may play an important role in the inhibitory regulation of ventricular contractility in the ferret in contrast to other mammalian species. The signal transduction process subsequent to agonist binding to A1 receptors including the pertussis toxin-sensitive G protein and ion channels may be responsible for the unique inhibitory action of adenosine in this species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169157
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Pharmacological characteristics of adenosine-induced inhibition of dog ventricular contractility: dependence on the pre-existing level of β-adrenoceptor activation (1991)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 344 (1991), S. 70-78 
    Details
    ISSN: 1432-1912
    Keywords: Adenosine ; Phenylisopropyladenosine ; Negative inotropic effect ; Cyclic AMP ; Ventricular myocardium of the dog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments were carried out to characterize the adenosine-induced negative inotropic effect in relation to the extent of β-adrenoceptor activation in the isolated dog left ventricular myocardium. Adenosine and R-N6-phenylisopropyladenosine inhibited the positive inotropic effect of isoprenaline (10−7 mol/1 and lower) about 20% of its maximal response, which was antagonized by an A1 adenosine receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine in a concentration-dependent manner. The negative inotropic effect of adenosine disappeared and that of R-N6-phenylisopro-pyl-adenosine decreased when the isoprenaline concentration was elevated to the level higher than 10−7 mol/1. Adenosine deaminase (1.5 U/ml) that abolished the negative inotropic effect of adenosine enhanced the effect of R-N6-phenylisopropyladenosine, indicating that endogenous adenosine released by high isoprenaline concentration (10−6 mol/1) modulates the interaction. The maximal response to adenosine and R-N6-phenylisopro-pyladenosine determined in the presence of 10−7 mol/1 isoprenaline was 50% of that of carbachol which elicited the maximal inhibition even in the presence of 10−6 mol/1 isoprenaline. The negative inotropic effects of R-N6-phenylisopropyladenosine and carbachol were additive to the maximal response equivalent to that of carbachol. The difference in the efficiency between the adenosine and muscarinic receptor agonists may be partly ascribed to the difference in densities of the respective receptors in the dog ventricular myocardium. The negative inotropic effect of R-N6-phenylisopropyladenosine in the presence of isoprenaline was associated with decrease in cyclic AMP levels elevated previously by isoprenaline. The elevation of cyclic AMP levels caused by isoprenaline (3 × 10−7 mol/1) was abolished by R-N6-phenylisopro-pyladenosine (10−4 mol/1), while the contractile response was reduced only by 30% with R-N6-phenylisopro-pyladenosine. In the absence of β-adrenoceptor stimulation R-N6-phenylisopropyladenosine elicited a negative inotropic effect without changes in cyclic AMP levels, but this effect was less than 10% of the basal force of contraction. It is concluded that in the dog ventricular myocardium adenosine receptors play a role for the inhibitory regulation of contractility, which is influenced markedly by the pre-existing level of β-adrenoceptor activation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167384
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    Paper (German National Licenses)
    Fulltext
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