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This Article Full Text Full Text (PDF) All Versions of this Article: 91/4/681    most recent expphysiol.2006.033175v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hleihel, W. Articles by Huchet-Cadiou, C. Search for Related Content PubMed PubMed Citation Articles by Hleihel, W. Articles by Huchet-Cadiou, C. Related Collections Heart/Cardiac Muscle

¹ Faculté de Médecine³ Faculté de Sciences et de Génie Informatique, Université Saint Esprit de Kaslik, BP 446 Jounieh, Lebanon ² Université de Nantes, CNRS, UMR 6204, Biotechnologie, Biocatalyse et Biorégulation, Faculté des Sciences et des Techniques, 2 rue de la Houssinière, BP 92208, F-44322 Nantes, France

In this study, it was shown that adenosine potentiates caffeine-induced Ca²⁺ release. It was then proposed that the enhancement of the caffeine-induced Ca²⁺ release might occur by a direct effect on the ryanodine Ca²⁺ release channel or on other Ca²⁺ regulation mechanisms. Furthermore, A_2A receptors may be functional on the ferret cardiac sarcoplasmic reticulum. Using chemically skinned fibres, experiments were conducted on ferret cardiac muscle to find out whether adenosine and the A₁ and A_2A adenosine receptor agonists (CCPA and CGS 21680) and antagonists (DPCPX and ZM 241385) affected caffeine-induced Ca²⁺ release and the Ca²⁺ sensitivity of contractile proteins. Changes in the caffeine-induced contracture brought about by adenosine and by adenosine-receptor agonists and antagonists were recorded in saponin-skinned fibres (50 µg ml^–1). Tension–pCa relationships were then obtained by exposing Triton X-100-skinned fibres (1% v/v) sequentially to solutions of decreasing pCa. Adenosine (1–100 nM) and the specific A_2A receptor agonist CGS 21680 (1–50 nM) produced a concentration-dependant potentiation of the caffeine-induced Ca²⁺ release from saponin-skinned fibres. The data plotted versus adenosine and CGS 21680 concentrations displayed sigmoid relationships (Hill relationship), with potentiation of Ca²⁺ release by 22.2 ± 1.6 (n = 6) and 10.9 ± 0.4% (n = 6), respectively. In addition, the potentiation of caffeine-induced Ca²⁺ release by adenosine (50 nM; 15.3 ± 1.0%; n = 6) and by CGS 21680 (50 nM; 11.2 ± 0.4%; n = 6) was reduced by the specific A_2A receptor antagonist ZM 241385 (50 nM) to 8.0 ± 1.4 (n = 4) and 5.4 ± 1.2% (n = 4), respectively. The A₁ receptor agonist CCPA (1–50 nM) and antagonist DPCPX (50 nM) had no significant effects on caffeine responses. In Triton X-100-skinned fibres, the maximal Ca²⁺-activated tension of the contractile proteins (41.3 ± 4.1 mN mm^–2; n = 8), the Hill coefficient (n_H = 2.2 ± 0.1; n = 8) and the pCa₅₀ (6.15 ± 0.05; n = 8) were not significantly modified by adenosine (100 nM) or by CGS 21680 (50 nM).

(Received 6 January 2006; accepted after revision 29 March 2006; first published online 31 March 2006)
Corresponding author W. Hleihel: Faculté Médecine, Université Saint Esprit de Kaslik, BP 446 Jounieh, Lebanon. Email: walidhleihel{at}usek.edu.lb