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Partial bladder outlet obstruction abolishes the receptor- and G protein-dependent increase in calcium sensitivity in rabbit bladder smooth muscle. Am J Physiol Renal Physiol 287: F682-F689, 2004. First published May 25, 2004; 10.1152/ajprenal.00117.2004.--Partial bladder outlet obstruction (PBOO) alters the function of the whole bladder and produces specific alterations in the contractility of the bladder smooth muscle cell. The goal of this study was to test the hypothesis that PBOO affects smooth muscle contraction at the level of the receptor- and G protein-dependent increase in myofilament [Ca.sup.2+] sensitivity. To address this question, we used [alpha]-toxin-permeabilized strips of bladder smooth muscle from control animals and animals subjected to 2 wk of PBOO. Increasing free [[Ca.sup.2+]] increased force in permeabilized strips from control animals; the addition of 10 [micro]M carbachol and 10 [micro]M GTP increased both the [Ca.sup.2+] sensitivity of the contractions and the maximal levels of force attained. In contrast, although increases in [[Ca.sup.2+]] increased force in permeabilized strips from PBOO animals, the addition of carbachol and GTP had no additional effects. Myosin light chain phosphorylation levels increased with [[Ca.sup.2+]], and although they tended to be higher in strips from PBOO animals, they did not reach statistical significance. Assessment of G protein activity from both animal models suggests this is not a site responsible for the loss of carbachol and GTP enhancement of myofilament [Ca.sup.2+] sensitivity. The addition of phorbol dibutyrate increased the [Ca.sup.2+] sensitivity of force development in strips from both animal models, suggesting that an alteration in PKC signaling is not involved. Our results are consistent with the hypothesis that PBOO decreases receptor-mediated myofilament calcium sensitization and that the site of action is downstream from either the G proteins or PKC. myosin light chain phosphorylation; guanosine 5'-O-(3-thiotriphosphate); protein kinase C; [alpha]-toxin permeabilization; phorbol dibutyrate

Partial bladder outlet obstruction in the rabbit produces changes in bladder function similar to those seen clinically in patients with obstructive uropathies. Whole organ function is significantly altered, as are the smooth muscle cells inside the bladder wall. This study was designed to determine whether outlet obstruction alters smooth muscle function at the level of contractile filaments. Rabbit bladders were partially obstructed for 2 wk. Triton X-100 was used to provide a detergent-skinned bladder smooth muscle preparation that would allow control of the intracellular environment while the ability to shorten and develop force is maintained. [Ca.sup.2+]-force and [Ca.sup.2+]-myosin light chain (MLC) phosphorylation relations and maximal velocity of shortening were determined. The [Ca.sup.2]+ sensitivity of force was significantly lower in tissues from animals subjected to outlet obstruction compared with tissues from control animals. In contrast, no difference was noted in the [Ca.sup.2]+ sensitivity of MLC phosphorylation. Maximal levels of stress and MLC phosphorylation were similar in both animal groups. Maximal velocity of shortening was significantly slower in tissues from outlet-obstructed animals at all [Ca.sup.2]+ concentrations compared with tissues from control animals. Ultrastructurally, detergent skinning had little effect on structural integrity. Moreover, tissues from obstructed animals showed an increase in the number of sarcolemmal attachment plaque structures. We suggest that partial bladder outlet obstruction produces deleterious (e.g., decrease in [Ca.sup.2]+ sensitivity of force) and compensatory (e.g., increase in membrane attachment plaques) changes in bladder smooth muscle cells. maximal velocity of shortening; Triton X-100 detergent-skinned fibers; attachment plaques; electron micrographs.

Bladder outlet obstruction secondary to benign prostate hyperplasia is associated with many cellular changes. This study was designed to determine whether these changes involve the contractile apparatus. Bladder smooth muscles from rabbits subjected to partial outlet obstruction for 2 wk were mounted for isometric force, isotonic shortening velocity, and myosin light chain (MLC) phosphorylation levels. Muscle strips from obstructed bladders exhibited spontaneous phasic activity; muscle strips from control bladders did not. Muscle strips from obstructed bladders exhibited increased sensitivity and higher levels of stress in response to the cumulative addition of KC1 or carbachol compared with control. During noncumulative addition of KC1 or carbachol, no differences in sensitivity were noted. Muscle strips from obstructed bladders had elevated basal MLC phosphorylation levels and stimulation produced small increases in MLC phosphorylation compared with control. [V.sub.max] during KC1 stimulation of muscle strips from obstructed bladders was 10-fold lower than control. Our results suggest that bladder out]et obstruction produces a muscle cell that develops higher levels of force but with greatly reduced cross bridge cycling rates. benign prostatic hyperplasia; shortening velocity; myosin light chain phosphorylation; carbachol

Partial bladder outlet obstruction in the rabbit produces changes in bladder function similar to those seen clinically in patients with obstructive uropathies. Whole organ function is significantly altered, as are the smooth muscle cells inside the bladder wall. This study was designed to determine whether outlet obstruction alters smooth muscle function at the level of contractile filaments. Rabbit bladders were partially obstructed for 2 wk. Triton X-100 was used to provide a detergent-skinned bladder smooth muscle preparation that would allow control of the intracellular environment while the ability to shorten and develop force is maintained. Ca[sup 2+]-force and Ca[sup 2+]-myosin light chain (MLC) phosphorylation relations and maximal velocity of shortening were determined. The Ca[sup 2+] sensitivity of force was significantly lower in tissues from animals subjected to outlet obstruction compared with tissues from control animals. In contrast, no difference was noted in the Ca[sup 2+] sensitivity of MLC phosphorylation. Maximal levels of stress and MLC phosphorylation were similar in both animal groups. Maximai velocity of shortening was significantly slower in tissues from outlet-obstructed animals at all Ca[sup 2+] concentrations compared with tissues from control animals. Ultrastructurally, detergent skinning had little effect on structural integrity. Moreover, tissues from obstructed animals showed an increase in the number of sarcolemmal attachment plaque structures. We suggest that partial bladder outlet obstruction produces deleterious (e.g., decrease in Ca[sup 2+] sensitivity of force) and compensatory (e.g., increase in membrane attachment plaques) changes in bladder smooth muscle cells. [ABSTRACT FROM AUTHOR]

Bladder outlet obstruction secondary to benign prostate hyperplasia is associated with many cellular changes. This study was designed to determine whether these changes involve the contractile apparatus. Bladder smooth muscles from rabbits subjected to partial outlet obstruction for 2 wk were mounted for isometric force, isotonic shortening velocity, and myosin light chain (MLC) phosphorylation levels. Muscle strips from obstructed bladders exhibited spontaneous phasic activity; muscle strips from control bladders did not. Muscle strips from obstructed bladders exhibited increased sensitivity and higher levels of stress in response to the cumulative addition of KCl or carbachol compared with control. During noncumulative addition of KCl or carbachol, no differences in sensitivity were noted. Muscle strips from obstructed bladders had elevated basal MLC phosphorylation levels and stimulation produced small increases in MLC phosphorylation compared with control. V[sub max] during KCl stimulation of muscle strips from obstructed bladders was 10-fold lower than control. Our results suggest that bladder outlet obstruction produces a muscle cell that develops higher levels of force but with greatly reduced cross bridge cycling rates. [ABSTRACT FROM AUTHOR]