Combined phosphoinositide and Ca2+ signals mediating receptor specificity toward neuronal Ca2+ channels.
Phosphatidylinositol 4,5-bisphosphate (PIP(2)) regulates Ca(2+) (I(Ca)) and M-type K(+) currents in superior cervical ganglion sympathetic neurons. In those cells, M(1) muscarinic and AT(1) angiotensin types do not elicit Ca(2+)(i) signals and suppress both currents via depletion of PIP(2), whereas the B(2) bradykinin and P2Y purinergic types elicit robust IP(3)-mediated [Ca(2+)](i) rises and neither deplete PIP(2) nor inhibit I(Ca). We have suggested that this specificity arises from differential Ca(2+)(i) signals underlying receptor-specific stimulation of PIP(2) synthesis by phosphatidylinositol (PI) 4-kinase. Here, we investigate which PI 4-kinase isoform underlies this signal, whether stimulation of PI 4-phosphate 5-kinase is also required, and the origin of receptor-specific Ca(2+)(i) signals. Recordings of I(Ca) were used as a PIP(2) "biosensor." In control, stimulation of M(1), but not B(2) or P2Y, receptors robustly suppressed I(Ca). However, when PI 4-kinase IIIβ, diacylglycerol kinase, Rho, or Rho-kinase was blocked, agonists of all three receptors robustly suppressed I(Ca). Overexpression of exogenous M(1) receptors yielded large [Ca(2+)](i) rises by muscarinic agonist, and transfection of wild-type IRBIT decreased Ca(2+)(i) signals, whereas dominant negative IRBIT-S68A had little effect on B(2) or P2Y responses but greatly increased muscarinic responses. We conclude that overlaid on microdomain organization is IRBIT, setting a "threshold" for [IP(3)], assisting in fidelity of receptor specificity.
Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229, USA.
Oleg
O
Zaika
Jie
J
Zhang
Mark S
MS
Shapiro
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002417:Cattle; D019852:Diacylglycerol Kinase / Q000378:metabolism; D005260:Female; D008297:Male; D015778:Minor Histocompatibility Antigens; D018721:Muscarinic Agonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000096:biosynthesis / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D013379:Substrate Specificity; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D015220:Calcium Channels; D015778:Minor Histocompatibility Antigens; D018721:Muscarinic Agonists; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D043562:Receptors, G-Protein-Coupled; D017853:Phosphotransferases (Alcohol Group Acceptor); D019852:Diacylglycerol Kinase; C402182:phosphatidylinositol phosphate 4-kinase; C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein; D002118:Calcium