Impact of Pseudomonas aeruginosa on Contractile Function in Porcine Coronary Artery

N-3-(oxododecanoyl)-L-homoserine lactone(3OC12-HSL), a major ‘quorum-sensing’ molecule produced by Pseudomonas aeruginosa is known to control the expression of virulence factors, and is also able to acutely inhibit vasoconstrictor tone in porcine isolated coronary artery (1). Presently, it is not clear whether this vascular action of 3OC12-HSL is of pathologically significance for the organism. Therefore, we have compared the effect of prolonged exposure to Pseudomonas aeruginosa (PAO1-L) and the mutant bacteria LasI (which do not produce 3OC12-HSL), on vasoconstrictor responses in porcine isolated coronary arteries.

PAO1-L and LasI, were revived from frozen glycerol stocks onto Low Salt Luria-Bertoni Agar plates. Segments (5mm) of the porcine coronary artery were then incubated for 18 hours with approximately 1.6 x 108 CFU/ml of either strain in 2ml Dulbecco’s Modified Eagle’s Medium (DMEM)at 37 °C. The coronary artery segments were then placed in 20ml Krebs-Henseleit solution, maintained at 37 °C and gassed with 95% O2/ 5% CO2, and placed under 100 milliNewtons (mN) resting tension for isometric tension recording. Preparations were contracted with 60mM KCl followed by increasing concentrations of the thromboxane-mimetic U46619 and the force generated determined (mN). The potency of U46619 was estimated as the logarithm of the concentration required to produce 50% of the maximum response (pEC50). All values were expressed as the mean ± standard error of the mean (S.E.M) in tissues from different animals (n). A student’s paired t-test was used to assess the statistical significance (p < 0.05) of any differences between mean values

Table 1 shows that the KCl responses of segments exposed for 18 hours to PAO1-LPseudomonas aeruginosa were significantly smaller than those exposed to the LasI type mutant strain. In contrast, neither the potency nor magnitude of responses to U46619 (Table 1) was different in PAO1-L incubated tissues(pEC50; 8.24 ± 0.09) compared to those exposed to LasI (8.40 ±0.14, n=6). Responses to 60mM KCl were assessed after 18 hours exposure to 30µM 3OC12-HSL but they were unaffected. The pEC50 value for U46619responses after overnight exposure to 30 µM 3OC12-HSL (8.26 ± 0.13, n=6) was also not significantly different compared to control segments (8.26 ± 0.13, n=6).

Table 1 The effects of incubation with PAO1-L and LasI strains of Pseudomonas aeruginosa and 30µM 3OC12-HSL on contractile responses (mN) of the porcine isolated coronary artery.

Overnight exposure of the coronary artery to Pseudomonas aeruginosa produced a selective reduction in the magnitude of contractions to KCl. Since this effect was not observed with either the mutant strain of Pseudomonas aeruginosa (LasI)or 3OC12-HSL per se, a factor unrelated to 3OC12-HSL appears to be implicated.

(1) Lawrence et al (1999) Br J Pharmacol, 128, 845-8.