Impaired β-adrenoceptor-induced relaxation in small mesenteric arteries from DOCA-salt hypertensive rats is due to reduced KCa channel activity

Abstract

β-Adrenoceptor (β-AR)-mediated relaxation plays an important role in the regulation of vascular tone. β-AR-mediated vascular relaxation is reduced in various disease states and aging. We hypothesized that β-AR-mediated vasodilatation is impaired in DOCA-salt hypertension due to alterations in the cAMP pathway. β-AR-mediated relaxation was determined in small mesenteric arteries from DOCA-salt hypertensive and control uninephrectomized (Uni) rats. To exclude nitric oxide (NO) and cyclooxygenase (COX) pathways, relaxation responses were determined in the presence of L-NNA and indomethacin, NO synthase inhibitor and COX inhibitors, respectively. Isoprenaline (ISO)-induced relaxation was reduced in arteries from DOCA-salt compared to Uni rats. Protein kinase A (PKA) inhibitors (H89 or Rp-cAMPS) or adenylyl cyclase inhibitor (SQ22536) did not abolish the difference in ISO-induced relaxation between the groups. Forskolin (adenylyl cyclase activator)-induced relaxation was similar between the groups. The inhibition of IKCa/SKCa channels (TRAM-34 plus UCL1684) or BKCa channels (iberiotoxin) reduced ISO-induced relaxation only in Uni rats and abolished the relaxation differences between the groups. The expression of SKCa channel was decreased in DOCA-salt arteries. The expression of BKCa channel α subunit was increased whereas the expression of BKCa channel β subunit was decreased in DOCA-salt arteries. The expression of receptor for activated C kinase 1 (RACK1), which is a binding protein for BKCa channel and negatively modulates its activity, was increased in DOCA-salt arteries. These results suggest that the impairment of β-AR-mediated relaxation in DOCA-salt mesenteric arteries may be attributable to altered IKCa/SKCa and/or BKCa channels activities rather than cAMP/PKA pathway. Impaired β-AR-stimulated BKCa channel activity may be due to the imbalance between its subunit expressions and RACK1 upregulation.

Inhibition of TLR4 attenuates vascular dysfunction and oxidative stress in diabetic rats

“…Ten micrograms of cellular protein was resolved by 10 % sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transferred to PVDF membranes (Thermo Scientific), as previously described [31,32], and probed with specific antibodies [TLR4 (Abcam # 22048), MyD88 (Cell Signaling #4283), Histone H3 (Cell Signaling #9715), GAPDH (Sigma #G9295), cyclooxygenase-2 (COX-2) (BD Transduction Laboratories #610203), and Na + /K + ATPase α1 (Cell Signaling #3010)]. The stripped membranes were later probed with β-actin antibody as a loading control.…”

“…Mesenteric arteries were then cut into rings (2 mm in length), mounted in a wire myograph for isometric tension recordings by a PowerLab 8/SP data acquisition system (ADInstruments Pty Ltd., Castle Hill, Australia), equilibrated in Krebs buffer for 30 min, and gassed with 5 % CO 2 in 95 % O 2 at 37°C, as described previously [31]. In all experiments, structural preservation of endothelium was confirmed by determining endothelial dependent relaxation to acetylcholine (ACh) in phenylephrine (PE) pre-contracting mesenteric ring preparations.…”

Mechanisms Underlying Enhanced Noradrenaline-Induced Femoral Arterial Contractions of Spontaneously Hypertensive Rats: Involvement of Endothelium-Derived Factors and Cyclooxygenase-Derived Prostanoids

“…[1][2][3] Because dysfunction and abnormal signaling in the main structural elements of the vasculature, such as endothelial cells and smooth muscle cells, are characteristic hypertension-associated vascular complications, [4][5][6][7][8][9] and functional impairments in these cells are observed in hypertensive patients and animal models of the disease, [10][11][12][13][14][15][16][17][18][19] a comprehensive understanding of the underlying mechanisms is indispensable for preventing and treating such complications.…”

“…TRAM-34 (an IK Ca inhibitor 12,26) ), 10 −7 M apamin (an SK Ca inhibitor 26) ), 10 −4 M VAS (a selective COX-1 inhibitor 34,35) ), 10 −6 M NS398 (a selective COX-2 inhibitor 34,35) ), before the cumulative addition of NAd or ACh. These drug concentrations were chosen based on previous studies.…”

Potassium Channels in Regulation of Vascular Smooth Muscle Contraction and Growth

“…Protein kinase A-dependent phosphorylation of the α-subunits also can activate BK Ca channels (Nara, Dhulipala, Wang, & Kotlikoff, 1998; Tian et al, 2004; Tian et al, 2001). Increased trafficking of the β1-subunits to the plasma membrane may also contribute to the mechanism of action of cAMP-related agonists (Matsumoto, Szasz, Tostes, & Webb, 2012). Vasodilators that act via cAMP and PKA increase BK Ca channel activity by increasing Ca 2+ spark activity (Porter et al, 1998; Wellman, Santana, Bonev, & Nelson, 2001; Yamaguchi, Kajita, & Madison, 1995).…”