Differential regulation of the InsP₃ receptor type-1 and -2 single channel properties by InsP₃, Ca²⁺ and ATP

J Physiol. 2012 Jul 15;590(14):3245-59. doi: 10.1113/jphysiol.2012.228320. Epub 2012 Apr 30.

Abstract

An elevation of intracellular Ca2+ levels as a result of InsP3 receptor (InsP3R) activity represents a ubiquitous signalling pathway controlling a wide variety of cellular events. InsP3R activity is tightly controlled by the levels of the primary ligands, InsP3, Ca2+ and ATP. Importantly, InsP3Rs are regulated by Ca2+ i in a biphasic manner. Ca2+ release through all InsP3R family members is also modulated dramatically by ATP, albeit with sub-type-specific properties. To ascertain if a common mechanism can account for ATP and Ca2+ regulation of these InsP3R family members, we examined the effects of [ATP] on the Ca2+ dependency of rat InsP3R-1 (rInsP3R-1) and mouse InsP3R-2 (mInsP3R-2) activity expressed in DT40-3KO cells. We used the on-nucleus patch clamp recording technique with various [ATP], [InsP3] and [Ca2+] in the patch pipette and measured single InsP3R channel activity in stably transfected DT40 cells. Under identical conditions, at saturating [InsP3] and [ATP], the activity of rInsP3R-1 and mInsP3R-2 was essentially identical in terms of single channel conductance, maximal achievable open probability (Po) and the [Ca2+] required for activation and inhibition of activity. However, in contrast to rInsP3R-1 at saturating [InsP3], the activity of mInsP3R-2 was unaffected by [ATP]. At lower [InsP3], ATP had dramatic effects on mInsP3R-2 Po, but unlike the rInsP3R-1, this did not occur by altering the relative Ca2+ dependency, but by simply increasing the maximally achievable Po at a particular [InsP3] and [Ca2+]. [InsP3] did not alter the biphasic regulation of activity by Ca2+ in either rInsP3R-1 or mInsP3R-2. Analysis of the single channel kinetics indicated that Ca2+ and ATP modulate the Po predominately by facilitating extended bursting activity of the channel but the underlying biophysical mechanism appears to be distinct for each receptor. Subtype-specific regulation of InsP3R channel activity probably contributes to the fidelity of Ca2+ signalling in cells expressing these receptor subtypes.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Animals
  • Calcium / metabolism*
  • Cell Line, Tumor
  • Chick Embryo
  • Inositol 1,4,5-Trisphosphate / metabolism*
  • Inositol 1,4,5-Trisphosphate Receptors / metabolism*
  • Ion Channel Gating*
  • Ligands
  • Mice
  • Potassium / metabolism
  • Protein Isoforms / metabolism
  • Rats

Substances

  • Inositol 1,4,5-Trisphosphate Receptors
  • Ligands
  • Protein Isoforms
  • Inositol 1,4,5-Trisphosphate
  • Adenosine Triphosphate
  • Potassium
  • Calcium