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This Article Full Text Full Text (PDF) All Versions of this Article: 296/4/C783    most recent 00452.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Camello-Almaraz, C. Articles by Pozo, M. J. Search for Related Content PubMed PubMed Citation Articles by Camello-Almaraz, C. Articles by Pozo, M. J.

MUSCLE CELL BIOLOGY AND CELL MOTILITY

Developmental changes in Ca²⁺ homeostasis and contractility in gallbladder smooth muscle

¹Department of Physiology, Nursing School, University of Extremadura, Caceres, Spain; and ²Graduate School of Pharmaceutical Sciences, Osaka University, Osaka, Japan

Submitted 2 September 2008 ; accepted in final form 3 February 2009

Relatively little is known about the contribution of Ca²⁺-dependent and -independent mechanisms in the contractility of neonatal gastrointestinal smooth muscle. We therefore studied Ca²⁺ homeostasis and Ca²⁺ sensitization mechanisms in 10-day-old and adult guinea pig gallbladder smooth muscle to elucidate developmental changes in these processes. Gallbladder contractility was evaluated by isometrical tension recordings from strips, intracellular Ca²⁺ concentration was estimated by epifluorescence microscopy of fura-2-loaded isolated cells, and protein expression and phosphorylation were assessed by Western blot analysis. The neonatal gallbladder contracted significantly less to CCK than adult tissue, but this correlated with an increased Ca²⁺ mobilization, suggesting immaturity of Ca²⁺ sensitization mechanisms. The enhanced Ca²⁺ release in the newborn gallbladder was the result of the increase in the size of the releasable Ca²⁺ pool. Moreover, in neonatal smooth muscle cells, neither the plasma membrane Ca²⁺ pump nor the Na⁺/Ca²⁺ exchanger collaborate in the extrusion of Ca²⁺. In contrast, in these cells, there is an increase in phospholamban phosphorylation, which could drive to an overactivity of the sarco(endo)plasmic reticulum Ca²⁺-ATPase pump. The reduced Ca²⁺ sensitivity in neonatal tissues was demonstrated by the lack of effect to Y-27362, an inhibitor of Rho kinase (ROCK), and GF-109203X, an inhibitor of PKC, on agonist-induced contraction. In addition, the neonatal gallbladder showed lower levels of RhoA, ROCK, PKC, and two effectors [C-kinase-dependent inhibitor of 17 kDa (CPI-17) and myosin phosphatase targetting 1 (MYPT1)] as well as an absence of CPI-17 and MYPT1 phosphorylation in response to agonists. In conclusion, our results indicate that the main mechanisms involved in smooth muscle contractility are under developmental regulation.

Ca²⁺-dependent contraction; Ca²⁺ sensitization; gastrointestinal smooth muscle