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Am J Physiol Regul Integr Comp Physiol (December 19, 2002). doi:10.1152/ajpregu.00596.2002
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Submitted on September 24, 2002
Accepted on December 13, 2002

LENGTH-DEPENDENT REGULATION OF BASAL MYOSIN PHOSPHORYLATION AND FORCE IN DETRUSOR SMOOTH MUSCLE

Paul H Ratz1* and Amy S Miner1

1 Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA, USA

* To whom correspondence should be addressed. E-mail: ratzph{at}evms.edu.

Urinary bladder (detrusor) smooth muscle is active in the absence of an external stimulus. Tone occurs even "at rest" during the filling phase, and is elevated in patients with overactive bladder. This study examined the role of muscle length on tone and the level of basal myosin light chain phosphorylation (MLC20P). MLC20P was 23.9 ± 1% (n = 58) at short lengths (zero preload; Lz). An increase in length from Lz to the optimum length for contraction (Lo) caused a reduction in MLC20Pto 15.8 ± 1% (n = 49). 10 µM staurosporine reduced MLC20P at Lz, but 1 µM staurosporine, a Ca2+-free solution, and inhibitors of MLC kinase, protein kinase C (PKC) and RhoA kinase (ROK) did not. However, 1 µM staurosporine and inhibitors of ROK inhibited LC20P and tone at Lo. These data support the hypothesis that a Ca2+-independent kinase, possibly ZIP-like kinase, regulates MLC20P at Lz, whereas in detrusor stretched to Lo, additional kinases, such as ROK, participate.




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