Proceedings of The Physiological Society
University of Edinburgh (2011) Proc Physiol Soc 25, C06 and PC06
Ablation and acute inhibition of Plasma Membrane Calcium ATPase 4 (PMCA4) with a novel inhibitor have different effects on isolated mouse mesenteric resistance arterial contractility
S. Lewis1, C. Cobb1, L. Neyses1, E. J. Cartwright1, C. Austin1
1. Cardiovascular Research Group, University of Manchester, Manchester, United Kingdom.
PMCA4 is a calcium extrusion pump which may also modulate Ca2+ -triggered signal transduction pathways. Previous studies postulate that PMCA4 modulates signalling via an interaction with neuronal nitric oxide synthase (nNOS) in localised plasmalemmal microdomains [1,2,3]. Although PMCA4 is the most abundant isoform in vascular smooth muscle its role is somewhat unclear [1,2]. Here, PMCA4 ablated mice (PMCA4KO) and a novel specific PMCA4 inhibitor (termed AP2)  were used to study the role of PMCA4 in resistance artery contractility. Contractility of isolated, pressurised (60mmHg), 3rd order mesenteric arteries from male PMCA4KO and wild type, (WT) mice in response to 100mM K+ depolarisation & noradrenaline (NA) (Log[NA] -9.0 to-5.0M) were determined. Passive lumen diameter and left & right wall thicknesses of arteries from PMAC4KO and WT mice were taken at transmural pressures of 5-140mmHg. Effects of acute PMCA4 inhibition with AP2 (10µM), nitric oxide synthase (NOS) inhibition with LNNA (100µM) & specific nNOS inhibition with Vinyl-L-Nio (10µM) were also investigated. Change in diameter is expressed as % of resting diameter. Data is expressed as mean+SEM. PMCA4 ablation had no effect on the magnitude of constrictions to 100mM K+ (PMCA4KO 53.2 ± 3.5% (n=11), WT 56.3 ± 3.6% (n=14)) or to noradrenaline (maximum constriction: PMCA4KO 59.5 ± 4.7% (n=11), WT 58.2 ± 2.5% (n=14)). Ablation of PMCA4 did not modulate the passive intra-lumen diameter, wall thickness, wall to lumen diameter or cross sectional area (CSA) of mesenteric arteries across the intravascular pressure range studied. A leftwards shift in the stress to strain relationship and significantly increased beta elastic modulus (β) were exhibited by arteries from PMCA4 KO mice compared to those from WT mice (β= PMCA4KO 10.03 ± 2.0 (n=19), WT 5.75 ± 0.64 (n=21)) suggesting ablation of PMCA4 increases mesenteric arterial stiffness. Acute PMCA4 inhibition with AP2, significantly reduced constriction to noradrenaline in arteries from wild type mice (maximum constriction: controls 70.6 ± 3.4% (n=8) and 63.8 ± 2.6% (n=10) in the absence and presence of AP2 respectively) but had no effect on arteries from PMCA4KO mice. Inhibitory effects of AP2 were reversed in arteries by NOS inhibition after LNNA incubation (AP2 61.8 ± 4.0% (n=8) and AP2+LNNA 69.2 ± 1.7% (n=10)) and also by nNOS inhibition with Vinly-L-Nio (AP2 61.8 ± 4.0% (n=8) and AP2+Vinyl-L-Nio 75.2 ± 1.3% (n=5)). Hence, PMCA4 inhibition with AP2 reduces vascular constriction by a nNOS-dependent mechanism. In conclusion, ablation and acute inhibition of PMCA4 with AP2 have different effects on mouse mesenteric resistance arterial contractility owing to the interaction with nNOS in localised plasmalemmal microdomains.
Where applicable, experiments conform with Society ethical requirements