Abstract
The physiological properties of mechanical response and the ultrastructure in the longitudinal body wall muscle (LBWM) of the opisthobranch mollusc Dolabella auricularia were studied to obtain information about excitation-contraction coupling in somatic smooth muscles responsible for smooth and slow body movement of molluscans. The contracture tension produced by 400 mM K was not affected by Mn ions (5--10 mM) and low pH (up to 4.0), but was reduced by procaine (2 mM). The K-contracture tension was not readily eliminated in a Ca-free solution containing ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'- tetraacetate (EGTA). A large contracture tension was also produced by rapid cooling of the surrounding fluid from 20 degrees to 5 degrees--3 degrees C even when the preparation showed no mechanical response to 400 mM K after prolonged (more than 2 h) soaking in the Ca-free solution. These results indicate that the LBWM fibers contain a large amount of intracellularly stored Ca which can be effectively released by membrane depolarization. The fibers were connected with each other, forming the gap junctions, the desmosomes, and the intermediate junctions. The sarcoplasmic reticulum (SR) consisted of vesicular and tubular elements, and was mostly located near the fiber surface. The plasma membrane showed marked tubular invaginations of 600-800 A in diameter, with many branches (surface tubules), extending inwards for approximately 2 micron. These surface tubules were closely apposed to the SR, and the bridgelike structures analogous to those in the triadic junction of vertebrate skeletal muscle were observed in the space between the surface tubules and the SR. It is suggested that the influence of membrane depolarization is transmitted inwards along the surface tubules to cause the release of Ca from the SR.
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Selected References
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- DEWEY M. M., BARR L. A STUDY OF THE STRUCTURE AND DISTRIBUTION OF THE NEXUS. J Cell Biol. 1964 Dec;23:553–585. doi: 10.1083/jcb.23.3.553. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Devine C. E., Somlyo A. V., Somlyo A. P. Sarcoplasmic reticulum and excitation-contraction coupling in mammalian smooth muscles. J Cell Biol. 1972 Mar;52(3):690–718. doi: 10.1083/jcb.52.3.690. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ebashi S., Endo M. Calcium ion and muscle contraction. Prog Biophys Mol Biol. 1968;18:123–183. doi: 10.1016/0079-6107(68)90023-0. [DOI] [PubMed] [Google Scholar]
- FARQUHAR M. G., PALADE G. E. Junctional complexes in various epithelia. J Cell Biol. 1963 May;17:375–412. doi: 10.1083/jcb.17.2.375. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kohlhardt M., Haap K., Figulla H. R. Influence of low extracellular pH upon the Ca inward current and isometric contractile force in mammalian ventricular myocardium. Pflugers Arch. 1976 Oct 15;366(1):31–38. doi: 10.1007/BF02486557. [DOI] [PubMed] [Google Scholar]
- Larsen W. J. Structural diversity of gap junctions. A review. Tissue Cell. 1977;9(3):373–394. doi: 10.1016/0040-8166(77)90001-5. [DOI] [PubMed] [Google Scholar]
- Peachey L. D. The sarcoplasmic reticulum and transverse tubules of the frog's sartorius. J Cell Biol. 1965 Jun;25(3 Suppl):209–231. doi: 10.1083/jcb.25.3.209. [DOI] [PubMed] [Google Scholar]
- Prescott L., Brightman M. W. The sarcolemma of Aplysia smooth muscle in freeze-fracture preparations. Tissue Cell. 1976;8(2):241–258. [PubMed] [Google Scholar]
- Sanger J. W., Hill R. B. Ultrastructure of the radula protractor of Busycon canaliculatum. Sarcolemmic tubules and sarcoplasmic reticulum. Z Zellforsch Mikrosk Anat. 1972;127(3):314–322. doi: 10.1007/BF00306876. [DOI] [PubMed] [Google Scholar]
- Sugi H., Matsubara I. Mechanical activity in the longitudinal body wall muscle of Dolabella auricura (mollusc). Comp Gen Pharmacol. 1970 Sep;1(3):349–357. doi: 10.1016/0010-4035(70)90029-7. [DOI] [PubMed] [Google Scholar]
- Suzuki S., Sugi H. Ultrastructural and physiological studies on the longitudinal body wall muscle of Dolabella auricularia. II. Localization of intracellular calcium and its translocation during mechanical activity. J Cell Biol. 1978 Nov;79(2 Pt 1):467–478. doi: 10.1083/jcb.79.2.467. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weber A., Herz R. The relationship between caffeine contracture of intact muscle and the effect of caffeine on reticulum. J Gen Physiol. 1968 Nov;52(5):750–759. doi: 10.1085/jgp.52.5.750. [DOI] [PMC free article] [PubMed] [Google Scholar]