QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Inoue, I. Articles by Bone, Q. Search for Related Content PubMed PubMed Citation Articles by Inoue, I. Articles by Bone, Q.

The Journal of Experimental Biology 205, 3535-3541 (2002)
Copyright © 2002 The Company of Biologists Limited

Excitation—contraction coupling in skeletal and caudal heart muscle of the hagfish Eptatretus burgeri Girard

Isao Inoue^1,2,*, Izuo Tsutsui^1,3 and Quentin Bone^1,4

¹ The Ine Marine Laboratory of National Institute for Physiological Sciences, Ine, Kyoto 626-0424, Japan
² Institute for Enzyme Research, Tokushima University, Tokushima 770-8503, Japan
³ Laboratory of Biology, Graduate School of Commerce and Management, Hitotsubashi University, Kunitachi, Tokyo 186-8601, Japan
⁴ Marine Biological Association of UK, Plymouth PL1 2PB, UK

^* Author for correspondence (e-mail: iinoue{at}ier.tokushima-u.ac.jp)

Accepted 21 August 2002

Hagfishes are regarded as the most primitive living craniates. Excitation—contraction (E—C) coupling mechanisms were studied in skeletal and caudal heart muscle fibres of the hagfish Eptatretus burgeri. In white (fast) skeletal muscle fibres from the musculus tubulatus, force generation in response to electrical stimulation was maintained in nominally Ca²⁺ free artificial seawater (ASW) (0Ca²⁺-ASW) containing 10 mmol l^-1 Co²⁺ (a blocker of Ca²⁺ currents). Similarly, in red (slow) fibres from parietal muscle bathed in 0Ca²⁺-ASW containing 10 mmol l^-1 Co²⁺, force generation occurred in association with K⁺ depolarisation when the external K⁺ concentration was increased to 100 mmol l^-1. Therefore, external Ca²⁺ is not required for muscle contraction. Hence, both white and red fibres possess the function of depolarisation-induced Ca²⁺-release from intracellular Ca²⁺ stores. This function is the same as in the skeletal muscle of all other vertebrates. In caudal heart muscle fibres, twitches in response to electrical stimuli were maintained in 0Ca²⁺-ASW containing 30 mmol l^-1 Co²⁺. In fibres loaded with fluo-3 bathed in 0Ca²⁺-ASW containing 30 mmol l^-1 Co²⁺, an increase in the intracellular free Ca²⁺ level associated with K⁺ depolarisation was observed after the external K⁺ concentration was increased to 100 mmol l^-1. Thus E—C coupling in the caudal heart muscle is also of the vertebrate skeletal muscle type.

Key words: excitation—contraction coupling, Ca²⁺, skeletal muscle, caudal muscle, hagfish, Eptatretus burgeri