Involvement of both G protein αs and βγ subunits in β-adrenergic stimulation of vascular L-type Ca 2+ channels

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Involvement of both G protein as and bg subunits in b-adrenergic stimulation of vascular L-type Ca 2+ channels 1

1 Previous data have shown that activation of b 3 -adrenoceptors stimulates vascular L-type Ca 2+ channels through a Gas-induced stimulation of the cyclic AMP/PKA pathway. The present study investigated whether b-adrenergic stimulation also uses the Gbg/PI3K/PKC pathway to modulate Ltype Ca 2+ channels in rat portal vein myocytes. 2 Peak Ba 2+ current (I Ba ) measured using the whole-cell patch clamp method was maximally increased by application of 10 mM isoprenaline after blockade of b 3 -adrenoceptors by 1 mM SR59230A. Under these conditions, the isoprenaline-induced stimulation of I Ba was reversed by ICI-118551 (a speci®c b 2 -adrenoceptor antagonist) but not by atenolol (a speci®c b 1 -adrenoceptor antagonist). The b 2 -adrenoceptor agonist salbutamol increased I Ba , an eect which was reversed by ICI-118551 whereas the b 1 -adrenoceptor agonist dobutamine had no eect on I Ba . 3 Application of PKA inhibitors (H-89 and Rp 8-Br-cyclic AMPs) or a PKC inhibitor (calphostin C) alone did not aect the b 2 -adrenergic stimulation of I Ba whereas simultaneous application of both PKA and PKC inhibitors completely blocked this stimulation. 4 The b 2 -adrenergic stimulation of L-type Ca 2+ channels was blocked by a pre-treatment with cholera toxin and by intracellular application of an anti-Gas antibody (directed against the carboxyl terminus of Gas). In the presence of H-89, intracellular infusion of an anti-Gb com antibody or a bARK 1 peptide as well as a pre-treatment with wortmannin (a PI3K inhibitor) blocked the b 2 -adrenergic stimulation of I Ba . 5 These results suggest that the b 2 -adrenergic stimulation of vascular L-type Ca 2+ channels involves both Gas and Gbg subunits which exert their stimulatory eects through PKA and PI3K/ PKC pathways, respectively

Modulation de l'excitabilité membranaire par les canaux calciques de type T

Les canaux calciques de type T sont associés aux activités rythmiques et aux décharges en bouffées dans les cellules excitables. Le clonage de 3 isotypes a soulevé l'hypothèse que chacun y serait différemment associé. Dans cette étude, nous avons observé des oscillations spontanées du potentiel (MPOs) corrélées à l'ouverture spontanée des canaux T selon l'isotype concerné, induisant une augmentation concomittante de la concentration de calcium intracellulaire. De nombreux arguments ont souligné l'importance du courant de fenêtre dans le déclenchement de ces activités rythmiques. De plus, nous avons déterminé les propriétés électrophysiologiques responsables de la forme et de la fréquence des MPOs. Enfin, nous avons montré que ces oscillations inhibaient d'autres voies de signalisation comme la réponse calcique à la bradykinine. En conclusion, ces données démontrent que chaque isotype de canaux T joue un rôle déterminant dans les activités rythmiques grâce à leur courant de fenêtre.T-type calcium channels are associated with pacemaker activity and burst firing in excitable cells. The cloning of three isotypes have raised the possibility that each one could differently participate to these phenomena. In our study, we have identified isotype-specific spontaneous opening of T-type calcium channels correlated with spontaneous oscillations of the membrane potential (MPOs), and concomitant increase of the intracellular calcium concentration ([Ca2+]. Several arguments have confirmed that these spontaneous rythmic activities were triggered by the T-type window current. Moreover, we have determined isotype-specific electrophysiological properties associated with the waveform and frequency of MPOs. Finally, we measured an inhibition of the amplitude of [Ca2]i response to bradykinin in cells exhibiting MPOs. Overall, these data demonstrate T-type calcium channels can play a primary role in pacemaker activity thanks to their isotype-specific window current.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Opium, opiacés, opioïdes (du remède millénaire à la physiologie des morphines endogènes)

BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Contribution of Ryanodine Receptor Subtype 3 to Ca 2+ Responses in Ca 2+ -overloaded Cultured Rat Portal Vein Myocytes

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Modulation of calcium signalling by dominant negative splice variant of ryanodine receptor subtype 3 in native smooth muscle cells

6sinoneThe ryanodine receptor subtype 3 (RYR3) is expressed ubiquitously but its physiological function varies from cell to cell. Here, we investigated the role of a dominant negative RYR3 isoform in Ca2+ signalling in native smooth muscle cells. We used intranuclear injection of antisense oligonucleotides to specifically inhibit endogenous RYR3 isoform expression. In mouse duodenum myocytes expressing RYR2 subtype and both spliced and non-spliced RYR3 isoforms, RYR2 and non-spliced RYR3 were activated by caffeine whereas the spliced RYR3 was not. Only RYR2 was responsible for the Ca2+-induced Ca2+ release mechanism that amplified Ca2+ influx- or inositol 1,4,5-trisphosphate-induced Ca2+ signals. However, the spliced RYR3 negatively regulated RYR2 leading to the decrease of amplitude and upstroke velocity of Ca2+ signals. Immunostaining in injected cells showed that the spliced RYR3 was principally expressed near the plasma membrane whilst the non-spliced isoform was revealed around the nucleus. This study shows for the first time that the short isoform of RYR3 controls Ca2+ release through RYR2 in native smooth muscle cells.noneDabertrand, F.;Morel, J.L.;Sorrentino, V.;Mironneau, J.;Mironneau, C.;Macrez, N.Dabertrand, F.; Morel, J. L.; Sorrentino, V.; Mironneau, J.; Mironneau, C.; Macrez, N

Phosphoinositide 3-Kinase Isoforms Selectively Couple Receptors to Vascular L-Type Ca 2+ Channels

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Phosphoinositide 3-Kinase γ Mediates Angiotensin II-induced Stimulation of L-type Calcium Channels in Vascular Myocytes

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