Involvement of Rho kinase and protein kinase C in carbachol‐induced calcium sensitization in β ‐escin skinned rat and guinea‐pig bladders

1 The signal transduction pathways involved in carbachol (CCh)‐induced calcium sensitization in β ‐escin permeabilized rat and guinea‐pig bladder smooth muscles were investigated and the results were compared with guinea‐pig taenia caecum. 2 Calcium contractions elicited cumulatively ( p Ca 7.5–5) in the presence of calmodulin were significantly increased in all three tissues when CCh (50  μ M ) was added to the medium. 3 Under constant [Ca 2+ ] i conditions ( p Ca 6), calmodulin (1  μ M ) and then GTP (100  μ M ) initiated significant contractions. CCh (50  μ M ) added to the bath caused a further contraction in all three tissues – calcium sensitization. This sensitization was significantly inhibited by atropine (50  μ M ). 4 The incubation of the tissues with the IP 3 ‐receptor blocker 2‐APB (30  μ M ) reduced the subsequent development of calcium sensitization by CCh in rat bladder but did not affect it in guinea‐pig bladder and taenia ceacum. 5 The Rho kinase (ROK) inhibitor Y‐27632 (5  μ M ) added in the presence of CCh reversed the calcium sensitization in rat bladder, whereas a transient contraction followed by a relaxation to a level not significantly different from the CCh contraction was seen in both guinea‐pig bladder and taenia caecum. Y‐27632 (1  μ M ) continuously present significantly inhibited the CCh‐induced Ca 2+ sensitization in rat bladder but not in guinea‐pig bladder or taenia caecum. 6 In the presence of cyclopiazonic acid (CPA) (1  μ M ) and calmodulin (1  μ M ), Y‐27632 (5  μ M ) did not change the calcium response curve (3 × 10 −7 –10 −5   M ) in rat bladder but increased the contractile responses significantly in both guinea‐pig bladder and taenia caecum. 7 The protein kinase C (PKC) inhibitor GF 109203X (5  μ M ) added in the presence of CCh inhibited the calcium sensitization induced by this muscarinic agonist in all three tissues in different ratios. 8 In conclusion, muscarinic receptor activation induces calcium sensitization in rat and guinea‐pig detrusor smooth muscles but there are differences in their pathways.British Journal of Pharmacology (2006) 148 , 376–384. doi: 10.1038/sj.bjp.0706723