title: SERCA pump optimizes Ca2+ release by a mechanism independent of store filling in smooth muscle cells.
abstract: Thapsigargin-sensitive sarco/endoplasmic reticulum Ca(2+) pumps (SERCAs) are involved in maintaining and replenishing agonist-sensitive internal stores. Although it has been assumed that release channels act independently of SERCA pumps, there are data suggesting the opposite. Our aim was to study the relationship between SERCA pumps and the release channels in smooth muscle cells. To this end, we have rapidly blocked SERCA pumps with thapsigargin, to avoid depletion of the internal Ca(2+) stores, and induced Ca(2+) release with either caffeine, to open ryanodine receptors, or acetylcholine, to open inositol 1,4,5-trisphosphate receptors. Blocking SERCA pumps produced smaller and slower agonist-induced [Ca(2+)](i) responses. We determined the Ca(2+) level of the internal stores both indirectly, measuring the frequency of spontaneous transient outward currents, and directly, using Mag-Fura-2, and demonstrated that the inhibition of SERCA pumps did not produce a reduction of the sarco/endoplasmic reticulum Ca(2+) levels to explain the decrease in the agonist-induced Ca(2+) responses. It appears that SERCA pumps are involved in sustaining agonist-induced Ca(2+) release by a mechanism that involves the modulation of Ca(2+) availability in the lumen of the internal stores.
authors.affiliation: Departamento de Bioquímica, CINVESTAV-IPN, México D.F., 07000, Mexico.
authors.forename: Leticia
authors.initials: L
authors.lastname: Gómez-Viquez
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Guerrero-Serna
authors.forename: Ubaldo
authors.initials: U
authors.lastname: García
authors.forename: Agustín
authors.initials: A
authors.lastname: Guerrero-Hernández
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D002478:Cells, Cultured; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology
chemical_list: D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium