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K Groschner

Publications and source records attributed to K Groschner.

48 records · Page 3Linked to original sources
PubMed1992

Increases in endothelial cyclic AMP levels amplify agonist-induced formation of endothelium-derived relaxing factor (EDRF).

The interaction between intracellular cyclic AMP and agonist-induced endothelium-derived relaxing factor (EDRF) (NO) formation was investigated in pig aortic endothelial cells. Three potent stimulators of adenylate cyclase, namely forskolin, adenosine and isoprenaline, amplified bradykinin- and ATP-induced biosynthesis and release of EDRF. None of the substances by itself affected basal EDRF formation. The effects of forskolin, adenosine and isoprenaline corresponded to an enhanced agonist-induced rise in intracellular free Ca2+ concentration ([Ca2+]i), were mimicked by the membrane-permeable cyclic AMP analogue dibutyryl cyclic AMP and were antagonized by the protein kinase inhibitor N-[2-(methylamino)ethyl]-5-isoquinolinesulphonamide dihydrochloride (H-8). Our data suggest that cyclic AMP-dependent phosphorylation modulates Ca(2+)-signalling and thus the function of endothelial cells. This mechanism may be of particular physiological importance, since it allows a joint regulation of endothelial functions by tissues factors such as bradykinin, which directly affects [Ca2+]i and agonists which affect intracellular cyclic AMP levels.

Adenosine↗
PubMed1992

Activation of a small-conductance Ca(2+)-dependent K+ channel contributes to bradykinin-induced stimulation of nitric oxide synthesis in pig aortic endothelial cells.

Bradykinin-induced K+ currents, membrane hyperpolarization, as well as rises in cytoplasmic Ca2+ and cGMP levels were studied in endothelial cells cultured from pig aorta. Exposure of endothelial cells to 1 microM bradykinin induced a whole-cell K+ current and activated a small-conductance (approximately 9 pS) K+ channel in on-cell patches. This K+ channel lacked voltage sensitivity, was activated by increasing the Ca2+ concentration at the cytoplasmic face of inside-out patches and blocked by extracellular tetrabutylammonium (TBA). Bradykinin concomitantly increased membrane potential and cytoplasmic Ca2+ of endothelial cells. In high (140 mM) extracellular K+ solution, as well as in the presence of the K(+)-channel blocker TBA (10 mM), bradykinin-induced membrane hyperpolarization was abolished and increases in cytoplasmic Ca2+ were reduced to a slight transient response. Bradykinin-induced rises in intracellular cGMP levels which reflect Ca(2+)-dependent formation of EDRF(NO) were clearly attenuated in the presence of TBA (10 mM). Our results suggest that bradykinin hyperpolarizes pig aortic endothelial cells by activation of small-conductance Ca(2+)-activated K+ channels. Opening of these K+ channels results in membrane hyperpolarization which promotes Ca2+ entry, and consequently, NO synthesis.

Animals↗
PubMed1992

SK&F 96365 inhibits histamine-induced formation of endothelium-derived relaxing factor in human endothelial cells.

Formation of endothelium-derived relaxing factor (EDRF) strictly correlates with the intracellular free Ca2+ ([Ca2+]i) concentration. We now demonstrate that the histamine-induced rise in [Ca2+]i of human umbilical vein endothelial cells is mostly due to activation of a membrane current which allows Ca2+ entry. This membrane current is sensitive to the novel inhibitor of agonist-induced Ca2+ entry, SK&F 96365, which blocked the histamine-induced sustained rise in [Ca2+]i, as well as 45Ca2+ uptake and membrane currents. Inhibition of the above cellular responses to histamine was accompanied by a considerable reduction of EDRF formation and release. Thus biosynthesis and release of EDRF from human umbilical vein endothelial cells significantly depend on agonist-induced Ca2+ entry involving receptor-operated Ca(2+)-permeable channels which can be blocked by SK&F 96365.

Calcium↗
PubMed1992

Voltage-sensitive chloride channels of large conductance in the membrane of pig aortic endothelial cells.

Single, large-conductance chloride-selective channels were studied in the membrane of pig aortic endothelial cells. These channels were usually inactive in cell-attached recordings and activated spontaneously upon formation of inside-out patches or amphotericin B-perforated vesicles. Channel activity was voltage dependent, with a maximum open probability within the range of -20 mV to + 20 mV. Addition of 1 mM Zn2+ to either the cytoplasmic or extracellular side blocked channel activity reversibly. Extracellular 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) blocked the channels; the concentration necessary for half-maximum blockade was 100 mumol/l. The frequency of observing channels in cell-attached patches increased from less than 5% to 27% when cells were treated for several minutes with 1 mumol/l bradykinin and to 80% in the presence of the calcium ionophore A23187 (1 mumol/l). Both agents increase the cytoplasmic Ca2+ concentration, thereby stimulating nitric oxide (NO) synthesis and cGMP formation in endothelial cells. Sodium nitroprusside (100 mumol/l), which spontaneously releases NO, did not increase Cl- channel activity in intact cells. Polymyxin B (100 mumol/l), an inhibitor of protein kinase C, clearly enhanced Cl- channel activity in intact cells, resulting in the observation of Cl- channels in 70% of cell-attached patches. Our results demonstrate the existence of a large-conductance (LC-type) Cl- channel in vascular endothelium which is subject to a complex cellular regulation, possibly involving inhibition via phosphorylation by protein kinase C, and activation by a Ca2(+)-dependent process which is different from the NO/cGMP pathway.

Amphotericin B↗
PubMed1991

Characterization of muscarinic receptors mediating endothelium-dependent relaxation of bovine coronary artery.

In order to identify the receptor subtype responsible for acetylcholine (ACh)-induced relaxation of bovine coronary artery, we determined the affinity of six subtype-selective muscarinic antagonists and compared them with affinity estimates obtained for bovine left atria. At low concentrations, ACh potently relaxed circular strips of coronary artery with endothelium (EC50 0.15 microM), but contracted them at higher agonist concentrations with potencies that depended on the presence or absence of endothelium: EC50 1.8 microM (without endothelium); 4.6 microM (with endothelium). The pA2 values obtained for antagonism of relaxant responses to ACh were: pirenzepine (M1-selective) 7.38 +/- 0.12; AF-DX 116 (11-[2-(diethylamino-methyl)-1-piperidinyl-acetyl]-5,11- dihydro-6H-pyrido(2,3-b)1,4-benzodiazepine-6-one; M2-selective) 5.79 +/- 0.09; and 4-diphenylacetoxy-N-methyl-piperidine-methobromide (4-DAMP; M3/M1-selective) 9.07 +/- 0.12. The corresponding Schild slopes were 0.98 +/- 0.07 for pirenzepine, 1.17 +/- 0.09 for AF-DX 116 and 1.01 +/- 0.04 for 4-DAMP. For the following three antagonists, pKB values were determined at two different antagonist concentrations: dicyclomine (M1-selective) 7.49 +/- 0.10, cyclohexylphenyl-(2-piperidinoethyl)-silanol (CPPS; M3-selective) 8.0 +/- 0.10, and parafluoro-hexahydrosila-difenidol (pFHHSiD; M3-selective) 7.87 +/- 0.10. For comparison, the antagonism of methacholine-induced negative inotropy in left atria was determined for three antagonists, yielding the following pA2 values: pirenzepine 5.98 +/- 0.14; AF-DX 116 6.81 +/- 0.14 and 4-DAMP 7.99 +/- 0.14. The slopes of the corresponding Schild plots were 1.05 +/- 0.10, 1.14 +/- 0.12 and 1.08 +/- 0.08, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1991

Ca2(+)-activated K+ channels in airway smooth muscle are inhibited by cytoplasmic adenosine triphosphate.

Large-conductance Ca2(+)-activated K+ channels were studied in membranes of cultured rabbit airway smooth muscle cells, using the patch-clamp technique. In cell-attached recordings, channel openings were rare and occurred only at very positive potentials. Bradykinin (10 microM), an agonist which releases Ca2+ from the sarcoplasmic reticulum, transiently increased channel activity. The metabolic blocker 2,4-dinitrophenol (20 microM), which lowers cellular adenosine triphosphate (ATP) levels, induced a sustained increase of channel activity in cell-attached patches. In excised patches, these channels had a slope conductance of 155 pS at 0 mV, were activated by depolarization and by increasing the Ca2+ concentration at the cytoplasmic side above 10(-7) mol/l. ATP, applied to the cytoplasmic side of the patches, dose-dependently decreased the channel's open-state probability. An inhibition constant (Ki) of 0.2 mmol/l was found for the ATP-induced inhibition. ATP reduced the Ca2+ sensitivity of the channel, shifting the Ca2+ activation curve to the right and additionally reducing its steepness. Our results demonstrate that cytoplasmic ATP inhibits a large-conductance Ca2(+)-activated K+ channel in airway smooth muscle. This ATP modulation of Ca2(+)-activated K+ channels might serve as an important mechanism linking energy status and the contractile state of the cells.

Adenosine Triphosphate↗
PubMed1991

The effects of the stereoisomers of propafenone and diprafenone in guinea-pig heart.

1. Optically pure enantiomers of propafenone and diprafenone were prepared from their racemic mixtures and tested for their ability to block beta-adrenoceptors and to prolong functional refractory period in the guinea-pig heart. beta-Adrenoceptor affinity of the enantiomers was determined by the radioligand binding technique and in functional experiments. 2. Propafenone and diprafenone inhibited specific binding of the beta-adrenoceptor antagonist (-)-[3H]-CGP-12177 to guinea-pig myocardial membranes. beta-Adrenoceptor affinities of diprafenone enantiomers exceeded those of corresponding propafenone enantiomers by one order of magnitude. Displacement of (-)-[3H]-CGP-12177 by both antiarrhythmics was highly stereoselective, in that the (S)-enantiomers were 40-60 fold, i.e. 1.6-1.8 log units more potent than the (R)-enantiomers. 3. Propafenone and diprafenone antagonized the positive inotropic action of isoprenaline in isolated atria. beta-Adrenoceptor antagonist potencies of diprafenone enantiomers were about one order of magnitude higher than those of corresponding propafenone enantiomers. For both drugs the (S)-enantiomer was found to be considerably more potent (14-40 fold) than the (R)-enantiomer. 4. Propafenone and diprafenone prolonged functional refractory period of isolated auricles with equal potency and no difference in the antiarrhythmic activity of purified enantiomers was found. 5. It is concluded that the enantiomers of propafenone and diprafenone exert comparable antiarrhythmic activity, whereas only (S)-enantiomers block cardiac beta-adrenoceptors with high affinity, which explains the beta-adrenoceptor antagonist effects of the racemic drugs.

Adrenergic beta-Antagonists↗
PubMed1990

ATP inhibits smooth muscle Ca2(+)-activated K+ channels.

There has been much recent interest in the roles played by smooth-muscle K+ channels in protecting cells against ischemic and anoxic insults and in therapeutic vaso- and bronchodilation (Buckingham 1990; Longmore & Weston 1990). A K+ channel, which is uniquely sensitive to cytoplasmic ATP (KATP), has been identified as a likely candidate for mediating these important functions (Standen et al. 1989). We now show, by using electrophysiological techniques in three different types of smooth muscle, that a large-conductance voltage and Ca2(+)-sensitive channel, otherwise indistinguishable from the the large-conductance Ca2(+)-activated K+ channel (BK channel), is also sensitive to cytoplasmic ATP and cromakalim. ATP, in a dose-dependent manner, decreased the probability of channel opening (Po) of rabbit aortic, rabbit tracheal and pig coronary artery BK channels with a Ki of 0.2-0.6 mM. Cromakalim, 10 microM, partially reversed the ATP induced inhibition and increased Po. Our observations raise the possibility that the ubiquitous BK channel may play a role during pathophysiological events.

Adenosine Triphosphate↗
PubMed1989

Interaction of DPI 201-106 with cardiac muscarinic receptors.

The effects of the new cardiotonic compound, DPI 201-106, on muscarinic responses and muscarinic receptor binding were studied in the guinea pig heart. DPI 201-106 exerted a pronounced anticholinergic action in isolated auricles and a moderate one in papillary muscles, which resembled the pattern of a functional antagonism. However, in competition binding experiments, DPI 201-106 inhibited binding of the specific muscarinic antagonist [3H]NMS with equal potency in atrial and ventricular homogenates (apparent KI = 0.7 mumol/l in atria and 1.2 mumol/l in ventricles). At higher concentrations (greater than 3 mumol/l), DPI 201-106 slowed the dissociation of [3H]NMS from cardiac muscarinic receptors, indicating that DPI 201-106 affects in addition a site allosteric to the muscarinic receptor. It is concluded that DPI 201-106 is able to inhibit cholinergic responses in the heart, not only by a functional antagonism but also by direct interaction with muscarinic receptors.

Animals↗
PubMed1989

Carbachol inhibits atrial contractility in the presence of potassium channel blocking agents.

To elucidate the role of potassium channel activation in muscarinic inhibition of atrial contractility, we studied the influence of K+ channel blockers on the effects of the muscarinic agonist carbachol in isolated guinea pig auricles. We tested BaCl2, tetraethylammoniumchloride (TEA), and 9-aminotetrahydroacridine (THA), which block K+ channels, for their ability to antagonize the effects of carbachol on atrial contractility and functional refractory period. Due to inhibition of K+ outward currents, BaCl2, TEA, and THA markedly blocked the carbachol-induced shortening of refractory period and, to a lesser extent, antagonized its negative inotropic action. BaCl2, TEA, and THA shifted the concentration-response curve of the negative inotropic action of carbachol to the right; the most pronounced effect was obtained with TEA (DR = 30 at 3 x 10(-3) M). The maximum negative inotropic effect of carbachol, however, was only slightly reduced by the K+ channel blockers, and carbachol clearly inhibited atrial contractility even in the absence of any shortening of refractory period. These results suggest the existence of an additional cholinergic, negative inotropic mechanism, distinctly different from activation of atrial K+ channels.

Animals↗
PubMedDate not supplied

Lack of second messenger function of cyclic GMP in acetylcholine-induced negative inotropism.

As cyclic 3',5'-guanosine monophosphate (cGMP) is still discussed as a possible mediator of the negative inotropic effects of cholinergic agents, the influence of acetylcholine (ACh) on force of contraction and cGMP tissue levels was studied in isolated, electrically driven guinea pig auricles in the presence of methylene blue, an inhibitor of guanylate cyclase activation, as well as of M & B 22,948, an inhibitor of cGMP breakdown. Nitroprusside-Na (NP), a potent stimulator of guanylate cyclase, was tested for comparison under the same conditions. ACh at concentrations of 10(-7)-5 X 10(-6) M dose-dependently diminished force of contraction down to cardiac arrest, whereas NP only had a slight negative inotropic effect that was maximum at 10(-5) M and reduced force of contraction to 89% of control. Although ACh was much more effective in reducing force of contraction than NP, only NP significantly increased myocardial cGMP levels. The rise in cGMP produced by NP was attenuated by methylene blue (5 X 10(-5) M) and augmented by M & B 22,948 (3.7 X 10(-4) M), whereas the contractile effects (similar as those of ACh) remained unchanged. These results suggest that the negative inotropic action of ACh is not mediated by cGMP.

Acetylcholine↗