Short term culture of blood vessel explants has gained increasing interest, as it provides opportunities for new approaches to studying biological function in an integrated in vitro cell system¹. As cell phenotype can change in culture, it is essential to understand how culture affects vessel function before employing it for studies with gene knockouts. We therefore undertook characterization of the pharmacological properties of mouse pulmonary artery explants during the first few days of culture. Intrapulmonary arteries (IPA) were harvested from Balb/c mice, divided into short segments and incubated in DMEM supplemented with 1% penicillin-streptomycin, 4.5 g/l glucose, L-glutamine, and 25mM HEPES, in 96 well plates placed in a humidified incubator at 37°C under 5% CO₂ in air. Responses to compounds known to modulate mechanical activity of IPA, and to ion channel blockers, were investigated in fresh tissue and explants after 48, 72 or 96 hours in culture, using wire myography. Data are expressed as mean ± s.e.m. of n experiments and compared using Student’s t-test. The contractile response to high potassium challenge (50mM KCl) was preserved up to 96 hours in culture. Responses to other agents are expressed as a percentage of the KCl response. Contraction to 10^-5M phenylephrine (PE) was also conserved: 144±5% (n=8) in fresh IPA; 117±35% (n=25) at 96h. Ca²⁺-free solution did not elicit a response in fresh IPA, but promoted an increasing relaxation after 48, 72 and 96h: respectively -5±1% (n=7), -70±37% (n=12) and -337±98% (n=25). IPA at 48h were more sensitive to 10mM KCl (76±6%, n=7) than fresh vessels (8±2%, n=8, P<4.10^-3). The TASK channel inhibitor, bupivicaine (10^-4M), caused increasing contraction from fresh IPA (4±5%, n=8) to 48h culture (65±5%, n=7), which dropped at 96h even to relaxation in some vessels (-27±39%, n=25). The Kv channel inhibitor 4-aminopyridine (4-AP; 10^-3M) elicited little contractile response in fresh vessels (7±1%, n=8), but pronounced contraction after 72 and 96h (respectively 104±22%, n=12, and 84±44%, n=25). Finally, although the L-type calcium channel blocker, nifedipine (10^-6M), had no effect on fresh IPA, it induced relaxation that increased with the duration of culture: -11±1% (n=4) at 48h; -33±12% (n=12) at 72h; -409±111% (n=25) at 96h. Our data show that mouse IPA remain responsive to KCl and PE up to 96 hours in culture. However, responses to Ca²⁺-free solution, nifedipine and 4-AP are modified in a manner that may be explained by progressive cell depolarisation during the culture. The data are consistent with recent work¹ where increased reactivity to high potassium challenge was observed in rat pulmonary artery cultured for 4 days.