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

This Article Full Text (PDF) 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 van der Kloot, W. Search for Related Content PubMed PubMed Citation Articles by van der Kloot, W.

1. For many years it has been known that when muscles are depolarized by raising [K⁺]_out there is an increase in respiration, even at levels of depolarization below the threshold for a detectable contracture.

2. K⁺-stimulated respiration occurs in muscles in which protein synthesis is blocked with puromycin. Stimulation does not depend upon activation of phosphorylase kinase. In muscle poisoned with IIA and kept in N₂, depolarizations below the threshold for contracture cause a fall in creatine phosphate. Apparently an ATPase is activated by depolarization; the resulting ADP is probably the trigger for the increase in oxygen uptake.

3. When the T-tubules are destroyed by the glycerol-osmotic shock method depolarization does not produce an increase in respiration.

4. Caffeine is known to stimulate respiration at concentrations below the threshold for producing a contracture. Muscles that have been made refractory to stimulation by potassium are still stimulated by caffeine: the action of caffeine is not antagonized by an increase in extracellular Mg²⁺. Caffeine must act on a later step in excitation—contraction coupling.

5. K⁺-stimulated respiration ultimately depends on the presence of Ca²⁺ in the Ringer. However, the Ca²⁺ can be replaced by Ni²⁺. It is known that Ni²⁺ does not activate actomyosin. Ni²⁺ is not sequestered by isolated fragments of the sarcoplasmic reticulum. It seems that the Ni²⁺ or Ca²⁺ in the extracellular solution is required for a superficial step in excitation—contraction coupling.

6. Respiration is also often stimulated when muscles are placed in an isotonic sucrose solution, even though the fibres are hyperpolarized. A trace amount of Ca²⁺ in the sucrose solution is probably necessary for the response.

7. An interaction between Ca²⁺ and a superficial membrane receptor appears to be an essential, early step in excitation—contraction coupling.