Regulation of inositol 1,4,5-trisphosphate receptors in rat basophilic leukemia cells. I. Multiple conformational states of the receptor in a microsomal preparation

Frederick C Mohr, Panda E C Hershey, Ildikó Zimányi, Isaac N Pessah

Research output: Contribution to journalArticle

11 Scopus citations


A detailed characterization of the inositol 1,4,5-trisphosphate (IP3) receptor in rat basophilic leukemia (RBL) cells, a neoplastic mast cell line, has been possible through the growth of solid RBL cell tumors which provide a rich source of IP3 receptor. Equilibrium binding studies show a 1.6 ± 0.1 pmol/mg of protein maximal binding capacity for [3H]IP3 at optimal Ca2+ (10 μM). The specificity of the RBL cell IP3 receptor towards phosphoinositides, ATP and heparin parallels those previously described with excitable and nonexcitable tissues. [3H]IP3 binding is slightly enhanced from < 1 nM to 10 μM Ca2+ and inhibited by > 10 μM Ca2+. Kinetic and equilibrium studies provide evidence for at least two classes or conformational states of binding sites with pico- and nanomolar affinities. At nM concentrations of IP3, neither binding to the IP3 receptor nor IP3-induced Ca2+ efflux from permeabilized cells demonstrates cooperativity. In contrast, at pM concentrations, IP3 binding kinetics deviate from simple mass action suggesting a complex interaction among binding sites for IP3 on the receptor-channel oligomer. The mechanism that regulate [3H]IP3 binding in RBL cells are unique when compared to what has been reported in other cells.

Original languageEnglish (US)
Pages (from-to)105-114
Number of pages10
JournalBBA - Biomembranes
Issue number1
StatePublished - Apr 8 1993



  • Calcium store
  • Inositol 1,4,5-trisphosphate
  • Intracellular calcium regulation
  • Mast cell
  • RBL cell

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology

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