Ca2+ sensitization in contraction of human bladder smooth muscle.

Abstract

The role of Ca2+ sensitization in the contraction of human bladder urinary smooth muscle (UBSM) was investigated. Simultaneous measurements of intracellular Ca2+ concentration ([Ca2+]i) and tension in fura-2 loaded intact strips and receptor coupled strips permeabilized with alpha-toxin were applied. Protein expressions was confirmed by Western blot analysis. In intact fura-2 loaded strips 1 microM carbachol (CCh) induced a greater contraction and a lower [Ca2+]i elevation than that induced by 60 mM K depolarization. In alpha-toxin permeabilized strips 1 microM CCh induced contraction at constant [Ca2+]i and produced a leftward shift in the [Ca2+]i-tension relationship. RhoA, Rho-associated kinase (ROCK) I, ROCK II and CPI-17 proteins were expressed in human UBSM. In intact fura-2 loaded strips the application of 3 microM Y-27632, a ROCK inhibitor, or 3 microM bisindolylmaleimide I (GF109203X), a protein kinase C inhibitor, during the sustained phase of contraction induced by 1 microM CCh induced relaxation without changing [Ca2+]i. In alpha-toxin permeabilized strips the application of 3 microM Y-27632 or 3 microM GF109203X during the sustained contraction induced by 0.3 microM Ca plus 10 microM guanosine triphosphate and 1 microM CCh induced relaxation at constant [Ca2+]i. These results indicate that in human UBSM CCh induces contraction, not only by increasing [Ca2+]i, but also by increasing the Ca2+ sensitivity of the contractile apparatus in a ROCK and protein kinase C dependent manner. Antagonism of Ca2+ sensitization pathways may represent an alternative target in the treatment of overactive bladder.