Suppression of Ca2+ influx by unfractionated heparin in non-excitable intact cells via multiple mechanisms.
Effect of unfractionated heparin (UFH), described as a cell-impermeant IP3 receptor antagonist, was studied on the capacitive Ca(2+) entry in non-permeabilized, intact cells, measuring the intracellular Ca(2+) levels using fluorescence microplate technique. Ca(2+) influx induced via Ca(2+) mobilization by histamine in Hela cells or evoked by store depletion with thapsigargin in RBL-2H3 cells was dose-dependently suppressed by UFH added either before or after the stimuli. UFH also prevented the spontaneous Ba(2+) entry indicating that the non-capacitive Ca(2+) channels may also be affected. In addition, UFH caused a significant and dose-dependent delay in Ca(2+), and other bivalent cation inflow after treatment of the cells with Triton X-100, but it did not diminish the amount of these cations indicating that UFH did not act simply as a cation chelator, but modulated the capacitive Ca(2+) entry possibly via store operated Ca(2+) channels (SOCCs). Inhibitory activities of UFH and 2-aminoethyl diphenyl borate on the capacitive Ca(2+) influx was found reversible, but the time courses of their actions were dissimilar suggesting distinct modes of action. It was also demonstrated using a fluorescence potentiometric dye that UFH had a considerable hyperpolarizing effect and could alter the changes of membrane potential during Ca(2+) influx after store depletion by thapsigargin. We presume that the hyperpolarizing property of this agent might contribute to the suppression of Ca(2+) influx. We concluded that UFH can negatively modulate SOCCs and also other non-capacitive Ca(2+) channels and these activities might also account for its multiple biological effects.
Németh
Klára
K
Department of Immunopharmacology, IVAX Drug Research Institute, 47-49 Berlini utca, H-1045 Budapest, Hungary. klara.nemeth@idri.hu <klara.nemeth@idri.hu>
Kurucz
István
I
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D006367:HeLa Cells; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism
D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D006493:Heparin