Sarcoplasmic reticulum, potassium, and cardiac force in rainbow trout and plaice.
The role played by the sarcoplasmic reticulum in force development and in cellular Ca2+ balance and its dependence on extracellular K+ were examined in heart ventricular tissue of rainbow trout and plaice. Compared with the steady-state twitch at a stimulation rate of 0.2 Hz, a 30-s rest led to a similar increase in twitch force in trout heart, regardless of whether [K+] was 2.5 or 5 mM. At 5 mM (but not at 2.5 mM) post-rest potentiation increased with increasing rest periods (from 30 to 900 s). These post-rest potentiations were removed or transformed into a loss of force by 10 microM ryanodine or 8 mM caffeine. In the plaice heart, where the sarcoplasmic reticulum is claimed to be sparse, the post-rest potentiation and the influence of ryanodine were small. The Ca2+ uptake measured during 5 min with 45Ca in the trout heart was higher in 5 than in 2.5 mM K+, regardless of the concomitant stimulation rate. This effect of K+ was removed by 10 microM ryanodine. The twitch force after 5 min of rest correlated significantly with the Ca2+ uptake, whereas the twitch force developed at a rate of 0.2 or 1.0 Hz did not. In conclusion, an elevation of K+ appears to stimulate the Ca2+ uptake of the sarcoplasmic reticulum. The twitch force after prolonged rest seems to relate to the Ca2+ contained in this organelle, whereas this does not apply to the twitch force developed at more physiological rates (0.2 or 1 Hz).
el-Sayed
M F
MF
Department of Zoophysiology, University of Aarhus, Denmark.
Gesser
H
H
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D005412:Flatfishes / Q000502:physiology*; D005432:Flounder / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D012487:Salmonidae / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*; D014337:Trout / Q000502:physiology*
D012433:Ryanodine; D002110:Caffeine; D011188:Potassium; D002118:Calcium