Complex effects of ryanodine on the sarcoplasmic reticulum Ca2+ levels in smooth muscle cells.
We have studied the effects of ryanodine and inhibition of the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA) with thapsigargin, on both [Ca(2+)](i) and the sarcoplasmic reticulum (SR) Ca(2+) level during caffeine-induced Ca(2+) release in single smooth muscle cells. Incubation with 10 microM ryanodine did not inhibit the first caffeine-induced [Ca(2+)](i) response, although it abolished the [Ca(2+)](i) response to a second application of caffeine. To assess whether ryanodine was inducing a permanent depletion of the internal Ca(2+) stores, we measured the SR Ca(2+) level with Mag-Fura-2. The magnitude of the caffeine-induced reduction in the SR Ca(2+) level was not augmented by incubating cells with 1 microM ryanodine. Moreover, on removal of caffeine, the SR Ca(2+) levels partially recovered in 61% of the cells due to the activity of thapsigargin-sensitive SERCA pumps. Unexpectedly, 10 microM ryanodine instead of inducing complete depletion of SR Ca(2+) stores markedly reduced the caffeine-induced SR Ca(2+) response. It was necessary to previously inhibit SERCA pumps with thapsigargin for ryanodine to be able to induce caffeine-triggered permanent depletion of SR Ca(2+) stores. These data suggest that the effect of ryanodine on smooth muscle SR Ca(2+) stores was markedly affected by the activity of SERCA pumps. Our data highlight the importance of directly measuring SR Ca(2+) levels to determine the effect of ryanodine on the internal Ca(2+) stores.
Gómez-Viquez
Leticia
L
Departamento de Fisiología Biofísica y Neurociencias, CINVESTAV-IPN, México.
Rueda
Angelica
A
García
Ubaldo
U
Guerrero-Hernández
Agustín
A
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000009:adverse effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D004791:Enzyme Inhibitors; D010726:Phosphodiesterase Inhibitors; D012433:Ryanodine; D002110:Caffeine; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium