Plasma Membrane Calcium ATPases (PMCAs’) are calcium extrusion pumps which may also modulate signal transduction. The most abundant PMCA isoform in vascular smooth muscle is PMCA4 however its effect on arterial constriction is unclear. Here, PMCA4 ablated mice (KO^−/−) and a novel specific PMCA4 inhibitor, AP2 were used to study effects of PMCA4 on arterial contractility. Vascular constrictor responses to 100mM potassium & noradrenaline (1x10⁻⁹M-3×10⁻⁵M) of isolated, pressurised mesenteric arteries from male PMCA4 KO^−/− and wild type, (WT^+/+) mice were determined by myography. Effects of acute PMCA4 inhibition with AP2, nitric oxide synthase (NOS) inhibition with N_ω-Nitro-L-arginine (LNNA) & neuronal NOS inhibition (nNOS) with Vinyl-L-Nio were also investigated. PMCA4 ablation had no effect on the magnitude of constrictions to 00mM K⁺ (KO^−/− 53.2% ± 3.5 n=11; WT^+/+ 56.3% ± 3.6 n=14) or noradrenaline (KO^−/− 59.5% ± 4.7 n=11; WT^+/+ 58.2% ± 2.5 n=14). PMCA4 inhibition with AP2, significantly attenuated constriction to noradrenaline in arteries from WT^+/+ mice (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 KO^−/− mice arteries. Inhibitory effects of AP2 were reversed in arteries by NOS inhibition with LNNA (AP2 treated 61.8% ± 4 n=8; AP2+LNNA treated 69.2% ± 1.7 n=10) and also by nNOS inhibition with Vinly-L-Nio (AP2 61.8% ± 4 n=8; AP2+Vinyl-L-Nio 75.2% ± 1.3 n=5). Therefore, PMCA4 inhibition with AP2 reduces vascular constriction by a nNOS-dependent mechanism. Ablation and acute inhibition of PMCA4 have different effects on mouse mesenteric arterial contractility.