Interaction of alpha1-adrenoceptor subtypes with different G proteins induces opposite effects on cardiac L-type Ca2+ channel.
We examined the effect of alpha(1)-adrenoceptor subtype-specific stimulation on L-type Ca2+ current (I(Ca)) and elucidated the subtype-specific intracellular mechanisms for the regulation of L-type Ca2+ channels in isolated rat ventricular myocytes. We confirmed the protein expression of alpha(1A)- and alpha(1B)-adrenoceptor subtypes at the transverse tubules (T-tubules) and found that simultaneous stimulation of these 2 receptor subtypes by nonsubtype selective agonist, phenylephrine, showed 2 opposite effects on I(Ca) (transient decrease followed by sustained increase). However, selective alpha(1A)-adrenoceptor stimulation (> or =0.1 micromol/L A61603) only potentiated I(Ca), and selective alpha(1B)-adrenoceptor stimulation (10 mumol/L phenylephrine with 2 micromol/L WB4101) only decreased I(Ca). The positive effect by alpha(1A)-adrenoceptor stimulation was blocked by the inhibition of phospholipase C (PLC), protein kinase C (PKC), or Ca2+/calmodulin-dependent protein kinase II (CaMKII). The negative effect by alpha(1B)-adrenoceptor stimulation disappeared after the treatment of pertussis toxin or by the prepulse depolarization, but was not attributable to the inhibition of cAMP-dependent pathway. The translocation of PKCdelta and epsilon to the T-tubules was observed only after alpha(1A)-adrenoceptor stimulation, but not after alpha(1B)-adrenoceptor stimulation. Immunoprecipitation analysis revealed that alpha(1A)-adrenoceptor was associated with G(q/11), but alpha(1B)-adrenoceptor interacted with one of the pertussis toxin-sensitive G proteins, G(o). These findings demonstrated that the interactions of alpha(1)-adrenoceptor subtypes with different G proteins elicit the formation of separate signaling cascades, which produce the opposite effects on I(Ca). The coupling of alpha(1A)-adrenoceptor with G(q/11)-PLC-PKC-CaMKII pathway potentiates I(Ca). In contrast, alpha(1B)-adrenoceptor interacts with G(o), of which the betagamma-complex might directly inhibit the channel activity at T-tubules.
O-Uchi
Jin
J
Department of Cell Physiology, The Jikei University School of Medicine, 3-25-8 Nishi-Shimbashi, Minato-ku, Tokyo 105-8461 Japan. o-uchi@jikei.ac.jp
Sasaki
Hiroyuki
H
Morimoto
Satoshi
S
Kusakari
Yoichiro
Y
Shinji
Hitomi
H
Obata
Toru
T
Hongo
Kenichi
K
Komukai
Kimiaki
K
Kurihara
Satoshi
S
D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D004146:Dioxanes / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006352:Heart Ventricles / Q000166:cytology; D007093:Imidazoles / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
C094643:A 61603; C547715:Adra1a protein, rat; C547718:Adra1b protein, rat; D020746:Calcium Channels, L-Type; D004146:Dioxanes; D004791:Enzyme Inhibitors; D007093:Imidazoles; D018340:Receptors, Adrenergic, alpha-1; D013764:Tetrahydronaphthalenes; D010656:Phenylephrine; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D037342:Pertussis Toxin; D011493:Protein Kinase C; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins