Focal adhesion kinase activation is involved in contractile stimulation-induced detrusor muscle contraction in mice

Recent studies suggest that smooth muscle contraction may involve mechanisms beyond myosin regulatory light chain (MLC) phosphorylation-induced actomyosin crossbridge cycling. This study aims to explore whether focal adhesion kinase (FAK) activation plays a role in mouse detrusor muscle contraction. Mouse detrusor muscle strips were preincubated with PF-573228 (2 μM), latrunculin B (1 μM), or vehicle (DMSO) for 30 minutes. The contractile responses to KCl (90 mM), electrical field stimulation (EFS, 2-32 Hz), or carbachol (CCh, 10^-7.5 to 10^-4.5 M) were measured. In a separate experiment, the levels of phosphorylated FAK (p-FAK) and MLC (p-MLC) were assessed in detrusor strips stimulated with CCh (10 μM) after incubation with PF-573228 or vehicle (DMSO), compared to those without CCh stimulation. Preincubation with PF-573228 or latrunculin B significantly reduced KCl-induced contractile responses compared to the vehicle-treated strips (p < 0.0001). EFS-induced contractile responses were significantly inhibited by PF-573228 at 8, 16, and 32 Hz (p < 0.05) and by latrunculin B at 16 and 32 Hz (p < 0.01). CCh-induced dose-response contractions were lower after preincubation with PF-573228 or latrunculin B compared to vehicle treatment (p = 0.0021 and 0.0003, respectively). Western blot analysis showed that CCh stimulation increased p-FAK and p-MLC expression, while PF-573228 preincubation prevented the increase in p-FAK but did not affect p-MLC. In conclusion, FAK activation plays a role in tension development induced by contractile stimulation in mouse detrusor muscle, likely through promoting actin polymerization rather than increasing MLC phosphorylation.