Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Calcitonin gene-related peptide (CGRP) elicits marked positive inotropic and chronotropic actions in the atria of several mammals. The second-messenger substance cyclic AMP and activation of L-type calcium channels have been implicated in these actions, but CGRP failed consistently to stimulate a contractile response in ventricular tissue obtained from various mammals. We assessed the actions of CGRP using isolated ventricular cardiomyocytes obtained from adult rats. Maximum changes in cell length (dL) of isolated cardiomyocytes during electrically stimulated (0.5 Hz) contractions were determined with adenosine deaminase (2.5 U/ml). In these conditions, CGRP produced a potent concentration-dependent positive contractile response that became maximal 4 min after initial stimulation. CGRP increased amplitude of cellular contractions maximally at a 1-nM concentration to a value 21.4% greater than that obtained without peptide. The EC50 value for the response was 31 pM. At concentrations greater than 1 nM, amplitude of the cellular contractile response decreased rapidly. The CGRP2-selective agonist, [cys ACM2,7] CGRP, increased the amplitude of cellular contractions maximally at 500 nM to a value 19.8% greater than that obtained without peptide. EC50 for this response was 6 nM. Salmon calcitonin (< or = 100 nM) did not elicit a significant contractile response. The fragment, CGRP8-37, a selective antagonist at the CGRP1 receptor subtype, while devoid of agonist activity, was a potent competitive antagonist of the positive contractile action of CGRP (pA2 value = 7.95). CGRP, present at maximally effective concentration (1 nM), when combined with isoprenaline ISO 100 pM-1 microM, elicited a greater increase in contractile amplitude than that elicited by ISO 100 pM-1 microM without CGRP. CGRP 1 nM combined with low concentrations of extracellular calcium ion < or = 4 mM produced a greater increase in contractile amplitude than that elicited by calcium ion < or = 4 mM without CGRP, but this additive effect was abolished in the presence of higher concentrations of extracellular calcium ion (> 4 mM). The cyclic AMP antagonist, Rp-cyclic AMPS (< or = 200 microM), did not inhibit the contractile response to CGRP 1 nM, but inhibited the contractile responses to ISO 100 nM and secretin 20 nM significantly and in a concentration-dependent manner. Diltiazem < or = 1 microM, a selective antagonist of L-type calcium channels, also failed to inhibit the contractile response to CGRP 1 nM but inhibited the contractile responses to ISO 100 nM and secretin 20 nM significantly and in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Calcitonin gene-related peptide stimulates a positive contractile response in rat ventricular cardiomyocytes. 752 74

Although secretin and vasoactive intestinal peptide (VIP) stimulate production of the second-messenger substance cyclic AMP and exert a positive inotropic action on rat ventricle in vitro, a direct action of these peptides on cardiomyocytes has not been established. In contrast to hearts of other mammalian species, which possess VIP-preferring receptors, rat heart is unique in that the existence of a "relatively nonselective receptor" at which both secretin and VIP may bind has been proposed. We wished to define the receptor(s) for secretin and VIP present on rat ventricular cardiomyocytes using a homogeneous suspension of viable cells. With adenosine deaminase 5 U/ml and the phosphodiesterase (PDE) inhibitor isobutyl methylxanthine (IBMX) 1 mM, both secretin and VIP increased intracellular levels of cyclic AMP maximally and concentration dependently after 5 min: EC50 values were 8 and 58 nM, respectively. At maximally effective concentrations, secretin 1 microM increased intracellular levels of cyclic AMP fourfold above basal levels, whereas a 1.6-fold increase was induced by VIP 10 microM. Maximum changes in cell length (dL) of isolated cardiomyocytes during electrically stimulated (0.5 Hz) contractions were determined in the presence of adenosine deaminase 2.5 U/ml. Under these conditions, both secretin and VIP produced a concentration-dependent positive contractile response that became maximal 5 min after addition of the peptide. Secretin 50 nM increased the amplitude of cellular contractions maximally to a value 37% greater than that obtained without peptide. VIP 20 nM increased the amplitude of cellular contractions maximally to a value 19% greater than that obtained without peptide. The EC50 values were 470 and 700 pM for VIP and secretin, respectively. The selective antagonist at VIP-preferring receptors, 4-Cl DPhe-6 Leu-17 VIP 10 microM did not antagonise the actions of VIP. In the presence of the selective antagonist at receptors for secretin, secretin 7-27 > or = 10 microM, the concentration dependence of the effect of secretin on accumulation of cellular cyclic AMP and contractile amplitude displayed a rightward parallel shift: the pA2 value for secretin 7-27 was 4.96. Secretin 7-27 also induced a rightward parallel shift of the concentration dependence of the actions of VIP. VIP 10 microM was additive with low concentrations of secretin (< 10 nM) in stimulating production of cyclic AMP but antagonised this response at higher concentrations of secretin (> 10 nM). Similarly, VIP 2 and 20 nM enhanced the contractile response to low concentrations of secretin (< 1 nM), but antagonised the response at higher concentrations of secretin (> 1 nM).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Secretin and vasoactive intestinal peptide are potent stimulants of cellular contraction and accumulation of cyclic AMP in rat ventricular cardiomyocytes. 752 89

Conventional inhibitors of cyclic AMP-dependent protein kinase lack membrane-permeability or selectivity, or both. The Rp diastereomer of adenosine cyclic 3',5'-phosphorothioate, Rp-cAMPS, is a novel membrane-permeable antagonist of cyclic AMP. We have assessed the ability of this compound to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile responses elicited in ventricular cardiomyocytes isolated from the hearts of adult rats. Cardiomyocytes were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM) and adenosine deaminase (5 units/ml). Contractile shortening was expressed as maximum shortening relative to prestimulus cell length (delta L%). In the presence of a maximally-effective concentration of isoprenaline (100 nM), which acts by a cyclic AMP-dependent mechanism, Rp-cAMPS inhibited the contractile response in a concentration-dependent and time-dependent manner. Following preincubation for 30 min with Rp-cAMPS (100 microM), the contractile response to isoprenaline (100 nM) was 14% of that elicited in the absence of this inhibitor. An incubation time of 30 min was chosen for all subsequent studies. Rp-cAMPS (< or = 200 microM) inhibited the contractile response to isoprenaline (100 nM) significantly and in a concentration-dependent manner, but failed to inhibit the contractile responses elicited by phenylephrine (2 microM) and calcium ion (7 mM) which act by cyclic AMP-independent mechanisms. In the presence of Rp-cAMPs (200 microM), the contractile response to isoprenaline (100 nM) was 24% of that in the absence of inhibitor. Rp-cAMPS was used subsequently to investigate the contractile-coupling mechanisms associated with some novel inotropic agents. Rp-cAMPS (< or = 200 microM) also inhibited the contractile responses to secretin (20 nM) and VIP (20 nM) significantly. In the presence of Rp-cAMPS (200 microM), the contractile response elicited by secretin (20 nM) was 19% of that in the absence of inhibitor, while that elicited by VIP (20 nM) was abolished completely. Rp-cAMPS (< or = 200 microM) failed to inhibit the contractile response elicited by CGRP (1 nM). In summary, Rp-cAMPS is a membrane-permeable, selective antagonist of cyclic AMP in ventricular cardiomyocytes and can be used, in conjunction with the bioassay of the intracellular accumulation of cyclic AMP, to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile coupling mechanisms in these cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Use of the cyclic AMP antagonist, Rp-cAMPS, to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile responses in rat ventricular cardiomyocytes. 789 68

Secretin, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) each exert potent positive contractile responses directly in rat ventricular cardiomyocytes. However, the contractile-coupling mechanisms associated with these responses have not been determined. In the present study, the involvement of L-type calcium channels in the contractile responses elicited by each peptide has been investigated using the selective antagonists at L-type calcium channels, verapamil and diltiazem. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of CaCl2 (2 mM) and adenosine deaminase (5U/ml). Cardiomyocytes were pre-incubated for 3 min prior to stimulation, in the absence of L-type calcium channel antagonist, and in the presence of verapamil (< or = 1 microM) or diltiazem (< or = 1 microM). Verapamil (< or = 1 microM) and diltiazem (< or = 1 microM) inhibited the contractile responses elicited by isoprenaline (100 nM) and forskolin (40 microM), used as positive controls, significantly, and in a concentration-dependent manner, but did not inhibit significantly the contractile response elicited by phenylephrine (2 microM), which was employed as a negative control. Verapamil (< or = 1 microM) and diltiazem (< or = 1 microM) inhibited the contractile responses to secretin (20 nM) and VIP (20 nM) significantly, and in a concentration-dependent manner, but did not inhibit the contractile response to CGRP. These data indicate that the positive contractile responses to secretin and VIP in mammalian ventricular cardiomyocytes involve the influx of calcium ion via L-type calcium channels, while the positive contractile response to CGRP does not.
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PMID:Inhibition by verapamil and diltiazem of agonist-stimulated contractile responses in mammalian ventricular cardiomyocytes. 852 57

1. G protein-coupled receptor kinases (GRKs) are thought to be important in mediating the agonist-induced phosphorylation and consequent desensitization of G protein-coupled receptor (GPCR) responses. We have previously shown that stable expression of a dominant negative mutant G protein-coupled receptor kinase 2 (GRK2) construct in NG108-15 mouse neuroblastoma x rat glioma cells suppresses the agonist-induced desensitization of A2A and A2B adenosine receptor-stimulated adenylyl cyclase activity (Mundell et al., 1997). To further determine the role of GRK2 in agonist-induced desensitization of these adenosine receptors, we stably overexpressed wild type GRK2 in NG108-15 cells. 2. In homogenates prepared from cells overexpressing GRK2, the acute stimulation of adenylyl cyclase by activation of A2A and A2B adenosine receptors was markedly reduced, but could be reversed by pretreating the cells with AD (adenosine deaminase), to remove extracellular adenosine from the medium. On the other hand, acute stimulation of adenylyl cyclase by secretin, iloprost, NaF and forskolin was the same in GRK2 overexpressing cells and plasmid-transfected control cells. 3. Cells overexpressing GRK2 were more sensitive to adenosine receptor agonist-induced desensitization than plasmid-transfected control cells. This effect was selective since the agonist sensitivity of desensitization for secretin and IP-prostanoid receptor-stimulated adenylyl cyclase activity was not affected by GRK2 overexpression. 4. These results further implicate GRK2 as the likely mechanism by which A2 adenosine receptors undergo short-term desensitization in NG108-15 cells, and indicate that even when overexpressed, GRK2 retains its substrate specificity for native receptors in intact cells. Furthermore, the susceptibility of GPCRs to desensitization appears to depend on the level of GRK expression, such that in cells that express high levels of GRK2, low agonist concentrations may be sufficient to trigger GRK-mediated desensitization.
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PMID:Enhanced expression of G protein-coupled receptor kinase 2 selectively increases the sensitivity of A2A adenosine receptors to agonist-induced desensitization. 978 8