In this study, we demonstrated that electroacupuncture can inhibit detrusor contraction and improve the function of rats with spinal cord injuries and revealed the important role of the ATP-P2X-p-MLCK/p-MLC pathway in mediating this effect.
In numerous clinical studies, surface electroacupuncture has been demonstrated to enhance urine storage capacity and urination efficiency in patients with neurogenic disorders following spinal cord injury16,17. Animal studies have further supported these findings by showing that electroacupuncture can increase bladder volume and decrease internal pressure in neurogenic rats4,18. Our study aligns with previous research, revealing that electroacupuncture effectively suppresses detrusor muscle contraction in neurogenic rats, leading to increased internal pressure and improved function.
Detrusor contraction is a fundamental pathological feature of neurogenic bladder following spinal cord injury. Clinical treatment of neurogenic bladder diseases often involves inhibiting detrusor contraction19,20。 Amend et al. demonstrated that antimuscarinic drugs can effectively increase bladder volume and detrusor compliance19 while Peyronnet et al. also supported this finding20. Li et al. utilized sacral nerve stimulation to modulate detrusor contraction and enhance function through nerve discharge21. These studies collectively highlight the effectiveness of inhibiting detrusor contraction in treating neurogenic bladder diseases. Our research indicated that acupuncture can effectively inhibit detrusor contraction and improve function. Importantly, acupuncture stands out for its high safety profile, minimal side effects, and cost-effectiveness compared to other therapies.
Numerous studies have demonstrated the substantial involvement of the purinergic ATP system in detrusor contraction8,22. This system is responsible for regulating the detrusor muscle by activating P2X1 and P2X2 receptors23. P2X1 and P2X2, known as ATP-gated nonselective cation channels, directly influence the ion channel state by altering the protein configuration, bypassing the need for rapid transduction through membranes and intracellular signaling24. Activation of the P2X1 and P2X2 receptors leads to the opening of cation channels, causing an influx of extracellular Ca2+ ions. Ca2+ ions combined with calmodulin (CaM) form a complex that, in turn, binds with myosin light chain kinase (MLCK) in the cytoplasm. This interaction activates MLCK, triggering detrusor contraction through the phosphorylation of myosin light chain (MLC). These findings highlight the crucial role of the ATP-P2X-p-MLCK/p-MLC pathway in regulating detrusor contraction (Fig. 6A).
The levels of ATP and its receptors P2X1 and P2X2 were found to be significantly higher in the model group than in the control group, with the exception of urodynamic indices, indicating their involvement in detrusor contraction. Conversely, the EA group exhibited significantly lower levels of ATP and its receptors P2X1 and P2X2 than the model group, suggesting that the ATP-P2X pathway may play a crucial role in the EA-induced inhibition of detrusor contraction. Furthermore, in the P2X inhibitor group, there was a significant reduction in ATP receptor expression, providing further evidence for the importance of the ATP-P2X pathway in the EA-mediated inhibition of detrusor contraction.
The results of our study demonstrated alterations in the phosphorylation levels of MLCK and MLC downstream of ATP in NB model rats, leading to increased expression of p-MLCK and p-MLC. These findings suggest that the ATP-P2X-p-MLCK/p-MLC pathway plays a crucial role in detrusor contraction. Following EA intervention, the changes in ATP-P2X-p-MLCK/p-MLC ratio and detrusor contraction were abrogated. Overall, our results indicate that EA effectively enhances detrusor relaxation by activating the ATP-P2X-p-MLCK/p-MLC pathway (Fig. 6B).
In this study, EA was administered at CV3, SP6, and BL32, as they are commonly used traditional acupuncture points for treating NB4. The tissues at CV3 are innervated by the T12-L1 segments of the spinal cord, while SP6 is innervated by the S2 segment. BL32 is situated in the second posterior sacral foramen, below the branch of the second sacral nerve. Acupuncture at the SP6 and BL32 can stimulate the second sacral nerve and regulate the S2-S4 parasympathetic center. Overall, acupuncture at these three sites together has been shown to improve excessive contraction of the bladder detrusor muscle in rats, possibly through modulation of the sympathetic and/or parasympathetic nerves innervating the bladder detrusor.18,25,26