title: Differential regulation of the InsP₃ receptor type-1 and -2 single channel properties by InsP₃, Ca²⁺ and ATP.
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.
authors.affiliation: Department of Pharmacology, School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, NY, USA.
authors.forename: Larry E
authors.initials: LE
authors.lastname: Wagner
authors.forename: David I
authors.initials: DI
authors.lastname: Yule
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D002642:Chick Embryo; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D015640:Ion Channel Gating; D008024:Ligands; D051379:Mice; D011188:Potassium / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats
chemical_list: D053496:Inositol 1,4,5-Trisphosphate Receptors; D008024:Ligands; D020033:Protein Isoforms; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium