alpha1-Adrenoceptors stimulate a Galphas protein and reduce the transient outward K+ current via a cAMP/PKA-mediated pathway in the rat heart.
alpha(1)-Adrenoceptor stimulation prolongs the duration of the cardiac action potentials and leads to positive inotropic effects by inhibiting the transient outward K(+) current (I(to)). In the present study, we have examined the role of several protein kinases and the G protein involved in I(to) inhibition in response to alpha(1)-adrenoceptor stimulation in isolated adult rat ventricular myocytes. Our findings exclude the classic alpha(1)-adrenergic pathway: activation of the G protein G(alphaq), phospholipase C (PLC), and protein kinase C (PKC), because neither PLC, nor PKC, nor G(alphaq) blockade prevents the alpha(1)-induced I(to) reduction. To the contrary, the alpha(1)-adrenoceptor does not inhibit I(to) in the presence of protein kinase A (PKA), adenylyl cyclase, or G(alphas) inhibitors. In addition, PKA and adenylyl cyclase activation inhibit I(to) to the same extent as phenylephrine. Finally, we have shown a functional coupling between the alpha(1)-adrenoceptor and G(alphas) in a physiological system. Moreover, this coupling seems to be compartmentalized, because the alpha(1)-adrenoceptor increases cAMP levels only in intact cells, but not in isolated membranes, and the effect on I(to) disappears when the cytoskeleton is disrupted. We conclude that alpha(1)-adrenoceptor stimulation reduces the amplitude of the I(to) by activating a G(alphas) protein and the cAMP/PKA signaling cascade, which in turn leads to I(to) channel phosphorylation.
Gallego
Mónica
M
Department of Physiology, School of Pharmacy, Universidad del País Vasco, Bilbao, Spain.
Setién
Raúl
R
Puebla
Lilian
L
Boyano-Adánez
María Del Carmen
Mdel C
Arilla
Eduardo
E
Casis
Oscar
O
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism
D000316:Adrenergic alpha-Agonists; D015221:Potassium Channels; D018340:Receptors, Adrenergic, alpha-1; D005576:Colforsin; D010656:Phenylephrine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010738:Type C Phospholipases; D019205:GTP-Binding Protein alpha Subunits, Gs; D011188:Potassium; D009638:Norepinephrine