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

Abstract

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 (pCa 7.5–5) in the presence of calmodulin were significantly increased in all three tissues when CCh (50 μM) was added to the medium. 3 Under constant [Ca²⁺]_i conditions (pCa 6), calmodulin (1 μM) and then GTP (100 μM) initiated significant contractions. CCh (50 μM) added to the bath caused a further contraction in all three tissues – calcium sensitization. This sensitization was significantly inhibited by atropine (50 μM). 4 The incubation of the tissues with the IP₃-receptor blocker 2-APB (30 μM) 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 μM) 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 μM) continuously present significantly inhibited the CCh-induced Ca²⁺ sensitization in rat bladder but not in guinea-pig bladder or taenia caecum. 6 In the presence of cyclopiazonic acid (CPA) (1 μM) and calmodulin (1 μM), Y-27632 (5 μM) 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 μM) 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