title: Altered sarcoplasmic reticulum calcium transport in the presence of the heavy metal chelator TPEN.
abstract: TPEN (N,N,N',N'-tetrakis(2-pyridylmethyl)-ethylenediamine) is a membrane-permeable heavy-metal ion chelator with a dissociation constant for Ca2+ comparable to the Ca2+ concentration ([Ca2+]) within the intracellular Ca2+ stores. It has been used as modulator of intracellular heavy metals and of free intraluminal [Ca2+], without influencing the cytosolic [Ca2+] that falls in the nanomolar range. In our previous studies, we gave evidence that TPEN modifies the Ca2+ homeostasis of striated muscle independent of this buffering ability. Here we describe the direct interaction of TPEN with the ryanodine receptor (RyR) Ca2+ release channel and the sarcoplasmic reticulum (SR) Ca2+ pump (SERCA). In lipid bilayers, at negative potentials and low [Ca2+], TPEN increased the open probability of RyR, while at positive potentials it inhibited channel activity. On permeabilized skeletal muscle fibers of the frog, but not of the rat, 50 microM TPEN increased the number of spontaneous Ca2+ sparks and induced propagating events with a velocity of 273 +/- 7 microm/s. Determining the hydrolytic activity of the SR revealed that TPEN inhibits the SERCA pump, with an IC(50) = 692 +/- 62 microM and a Hill coefficient of 0.88 +/- 0.10. These findings provide experimental evidence that TPEN directly modifies both the release of Ca2+ from and its reuptake into the SR.
authors.affiliation: Department of Physiology, Medical and Health Science Center, University of Debrecen, Nagyerdei krt. 98, H-4012 Debrecen, Hungary.
authors.forename: Mónika
authors.initials: M
authors.lastname: Sztretye
authors.forename: János
authors.initials: J
authors.lastname: Almássy
authors.forename: Tamás
authors.initials: T
authors.lastname: Deli
authors.forename: Péter
authors.initials: P
authors.lastname: Szentesi
authors.forename: Carole
authors.initials: C
authors.lastname: Jung
authors.forename: Beatrix
authors.initials: B
authors.lastname: Dienes
authors.forename: Cecilia A
authors.initials: CA
authors.lastname: Simut
authors.forename: Ernst
authors.initials: E
authors.lastname: Niggli
authors.forename: István
authors.initials: I
authors.lastname: Jona
authors.forename: László
authors.initials: L
authors.lastname: Csernoch
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D005029:Ethylenediamines / Q000378:metabolism* / Q000494:pharmacology; D007502:Iron Chelating Agents / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D011893:Rana esculenta; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D005029:Ethylenediamines; D007502:Iron Chelating Agents; D019837:Ryanodine Receptor Calcium Release Channel; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; C044387:N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine; D002118:Calcium