Mechano-sensitive linkage in excitation-contraction coupling in frog skeletal muscle.
1. Single skeletal muscle fibres of Xenopus laevis were used to investigate the involvement of a mechano-sensitive link in excitation-contraction coupling (EC coupling). 2. Fibres were stimulated by intermittent tetani until tension fell to about 40% of its initial level. Fibres were then stressed either by briefly stretching the fibres to 120% of their resting length or by exposing them to hypotonic Ringer solution ([NaCl] reduced to 80%) for 5 min. 3. In six of thirty-five stretched fibres and in all fourteen fibres exposed to hypotonic solution, a long-lasting depression of tension ensued. Tetanic tension then recovered slowly, often taking more than 10 h to return to its initial level. 4. During the period of minimal tension production, 12 mM caffeine induced a maximum contracture; 190 mM K+ induced a contracture larger than previous or subsequent tetani, and perchlorate (1 mM) slightly augmented tetanic tension. 5. Neither protease inhibitors nor a protein synthesis inhibitor altered the long-lasting period of tension depression and slow recovery. A free-radical scavenger was also without effect. 6. It is concluded that there is a mechano-sensitive link involved in EC coupling which can be damaged easily in fatigued muscle fibres.
Bruton
J D
JD
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Lännergren
J
J
Westerblad
H
H
D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D005609:Free Radicals; D007038:Hypotonic Solutions / Q000494:pharmacology; D008465:Mechanoreceptors / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation; D011480:Protease Inhibitors / Q000494:pharmacology; D013312:Stress, Physiological / Q000503:physiopathology; D014982:Xenopus laevis
D005609:Free Radicals; D007038:Hypotonic Solutions; D009124:Muscle Proteins; D011480:Protease Inhibitors