TY - JOUR

T1 - The α2 isoform of the Na,K-pump is important for intercellular communication, agonist-induced contraction, and EDHF-like response in rat mesenteric arteries

AU - Matchkov, Vladimir V

AU - Moeller-Nielsen, Nina

AU - Dam, Vibeke Secher

AU - Nourian, Zahra

AU - Briggs Boedtkjer, Donna M

AU - Aalkjaer, Christian

PY - 2012

Y1 - 2012

N2 - The specific role of different isoforms of the Na,K-pump in the vascular wall is still under debate. We have previously suggested that the α(2) isoform of the Na,K-pump (α(2)), Na(+), Ca(2+)-exchange (NCX), and connexin43 form a regulatory microdomain in smooth muscle cells (SMCs), which controls intercellular communication and contractile properties of the vascular wall. We have tested this hypothesis by downregulating α(2) in cultured SMCs and in small arteries with siRNA in vivo. Intercellular communication was assessed by using membrane capacitance measurements. Arteries transfected in vivo were tested for isometric and isobaric force development in vitro; [Ca(2+)](i) was measured simultaneously. Cultured rat SMCs were well-coupled electrically, but 10 μM ouabain uncoupled them. Downregulation of α(2) reduced electrical coupling between SMCs and made them insensitive to ouabain. Downregulation of α(2) in small arteries was accompanied with significant reduction in NCX expression. Acetylcholine-induced relaxation was not different between the groups, but the endothelium-dependent hyperpolarizing factor-like component of the response was significantly diminished in α(2)-downregulated arteries. Micromolar ouabain reduced in a concentration-dependent manner the amplitude of norepinephrine (NE)-induced vasomotion. Sixty percent of the α(2)-downregulated arteries did not have vasomotion, and vasomotion in the remaining 40% was ouabain insensitive. Although ouabain increased the sensitivity to NE in the control arteries, it had no effect on α(2)-downregulated arteries. In the presence of a low NE concentration the α(2)-downregulated arteries had higher [Ca(2+)](i) and tone. However, the NE EC50 was reduced under isometric conditions, and maximal contraction was reduced under isometric and isobaric conditions. The latter was caused by a reduced Ca(2+)-sensitivity. The α(2)-downregulated arteries also had reduced contraction to vasopressin, whereas the contractile response to high K(+) was not affected. Our results demonstrate the importance of α(2) for intercellular coupling in the vascular wall and its involvement in the regulation of vascular tone.

AB - The specific role of different isoforms of the Na,K-pump in the vascular wall is still under debate. We have previously suggested that the α(2) isoform of the Na,K-pump (α(2)), Na(+), Ca(2+)-exchange (NCX), and connexin43 form a regulatory microdomain in smooth muscle cells (SMCs), which controls intercellular communication and contractile properties of the vascular wall. We have tested this hypothesis by downregulating α(2) in cultured SMCs and in small arteries with siRNA in vivo. Intercellular communication was assessed by using membrane capacitance measurements. Arteries transfected in vivo were tested for isometric and isobaric force development in vitro; [Ca(2+)](i) was measured simultaneously. Cultured rat SMCs were well-coupled electrically, but 10 μM ouabain uncoupled them. Downregulation of α(2) reduced electrical coupling between SMCs and made them insensitive to ouabain. Downregulation of α(2) in small arteries was accompanied with significant reduction in NCX expression. Acetylcholine-induced relaxation was not different between the groups, but the endothelium-dependent hyperpolarizing factor-like component of the response was significantly diminished in α(2)-downregulated arteries. Micromolar ouabain reduced in a concentration-dependent manner the amplitude of norepinephrine (NE)-induced vasomotion. Sixty percent of the α(2)-downregulated arteries did not have vasomotion, and vasomotion in the remaining 40% was ouabain insensitive. Although ouabain increased the sensitivity to NE in the control arteries, it had no effect on α(2)-downregulated arteries. In the presence of a low NE concentration the α(2)-downregulated arteries had higher [Ca(2+)](i) and tone. However, the NE EC50 was reduced under isometric conditions, and maximal contraction was reduced under isometric and isobaric conditions. The latter was caused by a reduced Ca(2+)-sensitivity. The α(2)-downregulated arteries also had reduced contraction to vasopressin, whereas the contractile response to high K(+) was not affected. Our results demonstrate the importance of α(2) for intercellular coupling in the vascular wall and its involvement in the regulation of vascular tone.

KW - Animals

KW - Biological Factors

KW - Blotting, Western

KW - Cell Communication

KW - Connexin 43

KW - Down-Regulation

KW - Isomerism

KW - Isometric Contraction

KW - Male

KW - Membrane Potentials

KW - Mesenteric Arteries

KW - Muscle Contraction

KW - Muscle Tonus

KW - Muscle, Smooth, Vascular

KW - Myocytes, Smooth Muscle

KW - Patch-Clamp Techniques

KW - Polymerase Chain Reaction

KW - RNA, Small Interfering

KW - Rats

KW - Rats, Wistar

KW - Sodium-Calcium Exchanger

KW - Sodium-Potassium-Exchanging ATPase

KW - Transfection

KW - Vascular Capacitance

U2 - 10.1152/ajpheart.00673.2011

DO - 10.1152/ajpheart.00673.2011

M3 - Journal article

C2 - 22561302

VL - 303

SP - H36-46

JO - A J P: Heart and Circulatory Physiology (Online)

JF - A J P: Heart and Circulatory Physiology (Online)

SN - 1522-1539

IS - 1

ER -