title: Regulation of the type III InsP(3) receptor by InsP(3) and ATP.
abstract: Many hormones and neurotransmitters raise intracellular calcium (Ca(2+)) by generating InsP(3) and activating the inositol 1,4, 5-trisphosphate receptor (InsP(3)R). Multiple isoforms with distinct InsP(3) binding properties () have been identified (). The type III InsP(3)R lacks Ca(2+)-dependent inhibition, a property that makes it ideal for signal initiation (). Regulation of the type III InsP(3)R by InsP(3) and ATP was explored in detail using planar lipid bilayers. In comparison to the type I InsP(3)R, the type III InsP(3)R required a higher concentration of InsP(3) to reach maximal channel activity (EC(50) of 3.2 microM versus 0.5 microM for the types III and I InsP(3)R, respectively). However, the type III InsP(3)R did reach a 2.5-fold higher level of activity. Although activation by InsP(3) was isoform-specific, regulation by ATP was similar for both isoforms. In the presence of 2 microM InsP(3), low ATP concentrations (<6 mM) increased the open probability and mean open time. High ATP concentrations (>6 mM) decreased channel activity. These results illustrate the complex nature of type III InsP(3)R regulation. Enhanced channel activity in the presence of high InsP(3) may be important during periods of prolonged stimulation, whereas allosteric modulation by ATP may help to modulate intracellular Ca(2+) signaling.
authors.affiliation: Department of Physiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA. rob@hermen.med.yale.edu
authors.forename: R E
authors.initials: RE
authors.lastname: Hagar
authors.forename: B E
authors.initials: BE
authors.lastname: Ehrlich
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D020033:Protein Isoforms / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000378:metabolism*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate