Calyculin-A disrupts subplasmalemmal junction and recurring Ca2+ waves in vascular smooth muscle |
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Authors: | Lee Cheng-Han Kuo Kuo-Hsing Dai Jiazhen Leo Joyce M Seow Chun Yong Breemen Cornelis van |
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Affiliation: | The James Hogg iCAPTURE Centre for Cardiovascular and Pulmonary Research, University of British Columbia, St. Paul's Hospital, Room 166-1081 Burrard Street, Vancouver, BC, Canada V6Z 1Y6. |
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Abstract: | Excitation-contraction coupling (E-C coupling) in phenylephrine(PE)-stimulated rabbit inferior vena cava (IVC) depends on the generation of asynchronous recurring Ca2+ waves in the in situ vascular smooth muscle cells (VSMC). Previous studies by our group have implicated a putative non-selective cationic store-operated channel and the reverse-mode Na+-Ca2+ exchange in refilling of the intracellular Ca2+ store via the sarco/endoplasmic reticulum ATPase (SERCA) and the maintenance of the recurring Ca2+ waves. We hypothesize that for the proper functioning of these three Ca2+ translocators in the process of SR refilling, the plasma membrane (PM) and the underlying superficial sarcoplasmic reticulum (SR) form specialized PM-SR junctions, which are essential for the maintenance of the recurring Ca2+ waves. In order to test this hypothesis, calyculin-A, a serine/threonine phosphatase inhibitor that has been demonstrated to result in the disruption of the PM-SR junctions was used. In the control rabbit IVC, electron microscopy of the in situ VSMC indicates that 14.2+/-0.7% of the PM is closely apposed by the prominent superficial SR network, forming numerous flattened PM-SR junctional cytoplasmic spaces. In the control IVC stimulation with 5 microM PE resulted in sustained recurring Ca2+ waves with a frequency of 0.42+/-0.02 Hz. In calyculin-A treated rabbit IVC, a concentration-dependent dissociation of the superficial SR and loss of PM-SR junctions was observed. This progressive loss of the PM-SR junctions occurs over the same concentration range as the inhibition of PE-induced recurring Ca2+ waves. These findings offer support for the hypothesis that the presence of the PM-SR junctions is required for the generation of asynchronous recurring Ca2+ waves, which underlie excitation-contraction coupling in the VSMC of the rabbit IVC. |
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