Little is known about the involvement of receptor or non-receptor tyrosine kinases in contractile responses of pulmonary arteries. Intrapulmonary arteries (IPA) were obtained from the lungs of male Wistar rats. IPA were either treated with prostaglandin F_2α (PGF_2α, 20µM) and then snap-frozen for SDS-PAGE Western blot analysis (first and second order branches), or mounted on a wire myograph for measurement of isometric tension (second or third order branches). Experiments were performed at 37°C in bicarbonate-buffered physiological salt solution, pH 7.4, gassed with 5% CO₂/balance air. P values are derived from paired Student’s t test, unless otherwise stated. Using anti-phospho-tyrosine antibody (Cell Signalling) multiple protein bands were visualised, including ones at approximately 120, 90, 75 and 65 kD. Band intensities from PGF_2α-treated IPA were expressed as a percentage of those from paired untreated IPA. PGF_2α induced a 60-190% increase in tyrosine phosporylation. These increases were statistically significant (P<0.05 by analysis of 95% confidence interval, n = 8). All increases were reversed by the src-family kinase inhibitor PP2 (30µM, n = 5). PP2 (30µM) produced concentration-dependent relaxation of myograph-mounted IPA pre-contracted with 20 µM PGF_2α (45 ± 4% block, P< 0.01, n = 9), as did 10µM of the epidermal-growth-factor-receptor kinase inhibitor PD-174265 (60 ± 4% block, P< 0.001, n = 9). In FURA-PE3-loaded IPA, 30µM PP2 significantly inhibited the rise in intracellular Ca²⁺ concentration ([Ca²⁺]_i) induced by 0.1µM U46619 (51 ± 7% block, P<0.05, n = 7), but not that induced by 0.1µM PGF_2α (9 ± 12% block, N.S., n = 4). In addition, 30µM PP2 also relaxed PGF_2α contracted α-toxin permeabilised IPA, where [Ca²⁺]_i was clamped at pCa 6.8 (26 ± 2%, P< 0.05, n = 3). In conclusion, PGF_2α-mediated contraction in rat IPA is associated with tyrosine phosphorylation of multiple protein targets. Src-family kinase and EGFR-kinase activity are implicated. src-family kinases appear to influence contraction via both [Ca²⁺]_i-dependent and [Ca²⁺]_i-independent pathways.