cAMP-dependent protein kinase is in an active state in rat small arteries possessing a myogenic tone
Schubert, R.; Lehmann, G.; Serebryakov, V.N.; Mewes, H.; Hopp, H.H.
American Journal of Physiology 277(3): H1145-H1155
1999
ISSN/ISBN: 0002-9513 PMID: 10484437 Document Number: 504928
The hypothesis that cAMP-dependent protein kinase (protein kinase A; PKA) is in an active state in small arteries possessing a myogenic tone was investigated in pressurized rat tail small arteries. At a pressure of 80 mmHg, these vessels constricted to 71.6 ± 1.0% (n = 32) of the diameter of the fully relaxed state. The PKA inhibitors Rp-8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphothioate (Rp-CPT-cAMPS) and N-(2- amino -ethyl)-5- isoquinolinesulfonamide HCl (H-89) constricted these vessels dose dependently. For example, 300 mM Rp-CPT-cAMPS and 9 mM H-89 reduced vessel diameter by 11.0 ± 1.2% (n = 8) and 14.3 ± 3.6% (n = 5), respectively. The cGMP-dependent protein kinase (protein kinase G; PKG) inhibitor Rp-8-bromo-b-phenyl-1,N2-etheno-guanosine 3',5'-cyclic monophosphothioate (Rp-8-Br-PET-cGMPS) did not alter vessel diameter up to a concentration of 10 mM. Neither endothelium removal nor inhibition of neural transmission affected the action of Rp-CPT-cAMPS. The effect of 300 mM Rp-CPT-cAMPS was reduced by 82% after pretreatment of the vessel with 100 nM iberiotoxin, a blocker of calcium-activated potassium (KCa) channels. However, the effect of 300 mM Rp-CPT-cAMPS was not altered after pretreatment with 1 mM 4-aminopyridine, a blocker of delayed rectifier potassium channels, or 10 mM ryanodine, a blocker of ryanodine receptor-generated calcium sparks. In inside-out patch-clamp experiments on cells isolated from rat tail small arteries, 10 U/ml of the catalytic subunit of PKA together with 100 mM MgATP increased KCa channel activity 30.1 ± 9.8-fold (n = 9). Additionally, neither inhibition of PKA or PKG nor moderate activation of PKA or PKG altered the vessel response to a pressure step from 80 to 120 mmHg. These results suggest that in rat tail small arteries possessing a myogenic tone 1) PKA is in an active state modulating the level of the myogenic tone, and 2) KCa channels mediate, at least partly, this effect of PKA. Reprinted by permission of the publisher.