Reloading of Ca(2+)-depleted sarcoplasmic reticulum during rest in guinea pig ventricular myocytes.
The effects of rest on a Ca(2+)-depleted sarcoplasmic reticulum (SR) in guinea pig ventricular myocytes were investigated. Cell shortening was measured using a video edge-detection system, and cytoplasmic Ca2+ was monitored using the fluorescent indicator indo-1. Rapid cooling and rewarming in the presence of 10 mM caffeine were used to deplete the SR of Ca2+. The resting cell was then superfused for variable time intervals with a normal Tyrode solution containing 2 mM Ca2+. Another rapid cooling in caffeine was performed to assess the SR Ca2+ load at the end of rest. Rapid cooling after 1- and 2-min rest elicited an increase of indo-1 fluorescence of 51.9 +/- 7.7 (n = 17) and 72.7 +/- 6.7% of control (n = 9), respectively. This increase was not detectable when Ca2+ was absent from the superfusing solution. In contrast, the increase was larger when external Ca2+ was elevated to 4 mM. Nickel (5 mM) and nifedipine (20 microM) added to the superfusing solution during the rest interval did not alter the increase in indo-1 fluorescence. We conclude that Ca2+ is reaccumulated by a depleted SR during rest. Although this Ca2+ seems to originate from the extracellular space, its route from there to the SR is unclear.
Terracciano
C M
CM
Imperial College of Science, Technology and Medicine, National Heart and Lung Institute, London, United Kingdom.
MacLeod
K T
KT
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000172:deficiency* / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D003080:Cold Temperature; D006168:Guinea Pigs; D006352:Heart Ventricles; D007211:Indoles; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D009994:Osmolar Concentration; D012146:Rest; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D002121:Calcium Channel Blockers; D007211:Indoles; D002110:Caffeine; D009532:Nickel; D009543:Nifedipine; C048960:indo-1; D002118:Calcium