Evolution of Skeletal Muscle Excitation-Contraction Coupling and the Appearance of Dihydropyridine-Sensitive Intramembrane Charge Movement

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 255; no. 1343; pp. 181 - 187
• Main Authors: Inoue, Isao, Tsutsui, I., Bone, Quentin, Brown, Euan R.
• Format: Journal Article
• Language: English
• Published: London The Royal Society 22.02.1994
• Subjects: Contracture; Electric current; Electric potential; Invertebrates; Muscle fibers; Muscles; Pipettes; Skeletal muscle; Striated muscle; Vertebrates
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.1994.0026

Excitation-contraction (E-C) coupling was studied in the striated muscle fibres of lower chordates and invertebrates. In the agnathan Lampetra, twitches in response to electrical stimulation were unchanged after Ca2+ influx was blocked by the addition of Co2+. In the invertebrates examined (Branchiostoma, Oikopleura, Doliolum, Diphyes, Patinopecten and Sagitta), Ca2+ influx was necessary to cause a twitch. Whole-cell voltage clamp on muscle fibres of Lampetra revealed that intramembrane charge movement was partly blocked by 5 μm nifedipine, a dihydropyridine (DHP) derivative. Charge movement in fibres from Branchiostoma and Patinopecten was insensitive to nifedipine, although the Ca2+ current was 75% blocked by 5 μm nifedipine. The results suggest that the vertebrate type of E-C coupling was acquired between cephalochordates and agnathans, and was accompanied by the appearance of the DHP-sensitive component of intramembrane charge movement.