Phospholamban regulation of bladder contractility: evidence from gene-altered mouse models.
1. Phospholamban (PLB) is an inhibitor of the sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA). Its presence and/or functional significance in contractility of bladder, a smooth muscle tissue particularly dependent on SR function, is unknown. We investigated this by measuring the effects of carbachol (CCh) on force and [Ca2+]i in bladder from mice in which the PLB gene was ablated (PLB-KO mice). In the PLB-KO bladder, the maximum increases in [Ca2+]i and force were significantly decreased (41.5 and 47.4 % of WT), and the EC50 values increased. 2. Inhibition of SERCA with cyclopiazonic acid (CPA) abolished these differences between WT and PLB-KO bladder, localizing the effects to the SR. 3. To determine whether these effects were specific to PLB, we generated mice with smooth-muscle-specific expression of PLB (PLB-SMOE mice), using the SMP8 alpha-actin promoter. Western blot analysis of PLB-SMOE mice showed approximately an eightfold overexpression of PLB while SERCA was downregulated 12-fold. 4. In PLB-SMOE bladders, in contrast, the response of [Ca2+]i and force to CCh was significantly increased and the EC50 values were decreased. CPA had little affect on the CCh-induced increases in [Ca2+]i and force in PLB-SMOE bladder. 5. These results show that alteration of the PLB:SERCA ratio can significantly modulate smooth muscle [Ca2+]i. Importantly, our data show that PLB can play a major role in modulation of bladder contractility.
Nobe
K
K
Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0576, USA.
Sutliff
R L
RL
Kranias
E G
EG
Paul
R J
RJ
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015536:Down-Regulation / Q000502:physiology; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018721:Muscarinic Agonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D002217:Carbachol; D018721:Muscarinic Agonists; D000099211:Phospholamban