HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 290/2/C388    most recent 00409.2005v1 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 Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (17) Citing Articles via Google Scholar Google Scholar Articles by Morimura, K. Articles by Imaizumi, Y. Search for Related Content PubMed PubMed Citation Articles by Morimura, K. Articles by Imaizumi, Y.

MUSCLE CELL BIOLOGY AND CELL MOTILITY

Two-step Ca²⁺ intracellular release underlies excitation-contraction coupling in mouse urinary bladder myocytes

¹Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya; ²Department of Pharmacology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Toyama; and ³Cell Signaling & Ion Channel Research Group, Cellular Pharmacology, School of Pharmacy, Aichigakuin University, Nagoya, Japan

Submitted 12 August 2005 ; accepted in final form 19 September 2005

The relative contributions of Ca²⁺-induced Ca²⁺ release (CICR) versus Ca²⁺ influx through voltage-dependent Ca²⁺ channels (VDCCs) to excitation-contraction coupling has not been defined in most smooth muscle cells (SMCs). The present study was undertaken to address this issue in mouse urinary bladder (UB) smooth muscle cells (UBSMCs). Confocal Ca²⁺ images were obtained under voltage- or current-clamp conditions. When UBSMCs were activated by a 30-ms depolarization to 0 mV, intracellular Ca²⁺ concentration ([Ca²⁺]_i) increased in several small, discrete areas just beneath the cell membrane. These Ca²⁺ "hot spots" then spread slowly through the myoplasm as Ca²⁺ waves, which continued even after repolarization. Shorter depolarizations (5 ms) elicited only a few Ca²⁺ sparks, which declined quickly. The number of Ca²⁺ sparks, or hot spots, was closely related to the depolarization duration in the range of 5–20 ms. There was an apparent threshold depolarization duration of 10 ms within which to induce enough Ca²⁺ transients to spread globally and then induce a contraction. Application of 100 µM ryanodine to the pipette solution did not change the resting [Ca²⁺]_i or the VDCC current, but it did abolish Ca²⁺ hot spots elicited by depolarization. Application of 3 µM xestospongin C reduced ACh-induced Ca²⁺ release but did not affect depolarization-induced Ca²⁺ events. The addition of 100 µM ryanodine to tissue segments markedly reduced the amplitude of contractions triggered by direct electrical stimulation. In conclusion, global [Ca²⁺]_i rise triggered by a single action potential is not due mainly to Ca²⁺ influx through VDCCs but is attributable to the subsequent two-step CICR.

Ca²⁺-induced Ca²⁺ release; Ca²⁺-activated K⁺ current; voltage-dependent Ca²⁺ channel

This article has been cited by other articles:

				H. Cheng and W. J. Lederer Calcium Sparks Physiol Rev, October 1, 2008; 88(4): 1491 - 1545. [Abstract] [Full Text] [PDF]

				L. Balasubramanian, A. Ahmed, C.-M. Lo, J. S. K. Sham, and K.-P. Yip Integrin-mediated mechanotransduction in renal vascular smooth muscle cells: activation of calcium sparks Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2007; 293(4): R1586 - R1594. [Abstract] [Full Text] [PDF]

				S. Hotta, K. Morimura, S. Ohya, K. Muraki, H. Takeshima, and Y. Imaizumi Ryanodine receptor type 2 deficiency changes excitation-contraction coupling and membrane potential in urinary bladder smooth muscle J. Physiol., July 15, 2007; 582(2): 489 - 506. [Abstract] [Full Text] [PDF]

				B. S. Hu, L. K. Landeen, N. Aroonsakool, and W. R. Giles An analysis of the effects of stretch on IGF-I secretion from rat ventricular fibroblasts Am J Physiol Heart Circ Physiol, July 1, 2007; 293(1): H677 - H683. [Abstract] [Full Text] [PDF]