Obstruction enhances rho-kinase pathway and diminishes protein kinase C pathway in carbachol-induced calcium sensitization in contraction of α-toxin permeabilized guinea pig detrusor smooth muscle

Aims We investigated the relative important role of rho kinase (ROK) and protein kinase C (PKC) pathways in carbachol (CCh)-induced Ca ²⁺ sensitization in α-toxin permeabilized Guinea pig detrusor smooth muscle (DSM) following bladder outlet obstruction (BOO). Methods Bladder outlet obstruction was created by placement of a silver jeweler's jump rings loosely round the urethro-vesical junction of Guinea pigs. Sham operated Guinea pig underwent a similar protocol without application of the ring and served as control. α-Toxin permeabilized DSM strips from control Guinea pigs and those subjected to 6-8 weeks of BOO were mounted horizontally for isometric force recording in 100μl relaxing solution on perspex block. The effect of ROK inhibitor (Y-27632) and PKC inhibitor (GF-109203X) on CCh-induced Ca ²⁺ sensitization was studied during sustained contraction. Permeabilized DSM strips were also stimulated by cumulative increase of Ca ²⁺ concentration compared to that in control in the presence and in the absence of sensitization-induced PKC activator, phorbol 12,13-dibutyrate. Results Ca ²⁺ sensitization-induced by CCh was greater in BOO compared to controls. This muscarinic agonist-induced Ca ²⁺ sensitization was inhibited by Y-27632 or GF-109203X. The inhibitory effect of Y-27632 (5μM) was greater while the inhibitory effect of GF-109203X (5μM) was smaller in BOO compared to that in controls. Phorbol 12,13-dibutyrate (1μM) markedly increased Ca ²⁺ sensitivity in controls but not in BOO. Conclusions Our findings provide the first evidence that BOO enhances the ROK pathway and diminishes the PKC pathway in CCh-induced Ca ²⁺ sensitization in contraction of permeabilized Guinea pig DSM and suggest that inhibitors of ROK might potentially relieve bladder dysfunction related to BOO.