Repletion of sarcoplasmic reticulum Ca after ryanodine in rat ventricular myocytes.
The ryanodine (R)-induced loss of sarcoplasmic reticulum (SR) Ca2+ and the abilities of the SR to accumulate Ca2+ and participate in contractile activation after R were studied in rat ventricular myocytes. Indo 1 fluorescence (IF) indexed cytosolic Ca2+, and caffeine assayed SR Ca2+. Before R, there was a negative staircase, and the SR accumulated Ca2+ at rest. During stimulation (0.5 Hz), R decreased IF and contraction, converting the negative staircase to positive. When R was pulsed onto resting cells, IF increased and cells shortened, subsequently behaving as if stimulated in R. After R, there was no caffeine-releasable Ca2+ at rest, and little accumulated during 0.5-Hz stimulation. At high rates, caffeine-releasable Ca2+ and diastolic IF increased. In isoproterenol and R, IF transients and contractions recovered at 0.5 Hz with a marked positive staircase and little diastolic IF increase. Within 10 beats, SR Ca2+ accumulated to pre-R levels. R eliminated the positive inotropic effect of paired-pulse stimulation, but isoproterenol temporarily restored it. Twitch contractions in thapsigargin, an SR Ca2+ pump blocker, and isoproterenol were slow compared with control or R + isoproterenol. R leaks SR Ca2+ into the cytosol. SR Ca2+ can be repleted in R by high-rate stimulation or by low-rate stimulation with a beta-adrenergic agonist. SR Ca2+ release in R can be temporarily restored if Ca2+ influx and SR Ca2+ pumping are increased enough to overcome the SR Ca2+ leak.
duBell
W H
WH
Laboratory of Cardiovascular Science, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224.
Lewartowski
B
B
Spurgeon
H A
HA
Silverman
H S
HS
Lakatta
E G
EG
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D006352:Heart Ventricles; D007211:Indoles; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D007211:Indoles; D013729:Terpenes; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D007545:Isoproterenol; C048960:indo-1; D002118:Calcium