Mechanisms of angiotensin II-mediated decreases in intraneuronal Ca2+ in calcium-loaded stellate ganglion neurons.
Our laboratory has reported previously that angiotensin II, type-1 (AT(1)) receptor stimulation in isolated stellate ganglion neurons decreases intraneuronal calcium concentration ([Ca(2+)]i) acutely if baseline [Ca(2+)]i is high and increases [Ca(2+)]i if baseline [Ca(2+)]i is low. Part of the angiotensin II (Ang II) effect in high Ca(2+) neurons is mediated through stimulation of Na(+)-Ca(2+) exchange. Current experiments were conducted to identify additional steps in the signaling pathways. In Ca(2+)-loaded neurons, Ang II-induced decreases in [Ca(2+)]i were attenuated by phospholipase C inhibition (U73122) or nitric oxide (NO) synthase inhibition (L-NMMA) and were mimicked by the cGMP analogue 8-Br-cGMP. Protein kinase C (PKC) inhibition (bisindolylmaleimide I or Go6976) and protein kinase G (PKG) inhibition (KT5823) partially blocked Ang II-mediated decreases in [Ca(2+)]i, but complete blockade of Ang II effects was obtained with combined PKC and PKG inhibition. Modulation of inositol triphosphate (IP(3))-inducible ER Ca(2+) release by [Ca(2+)]i was investigated using furaptra, an ER-retaining dye. IP(3)-mediated ER Ca(2+) release in beta-escin-permeabilized neurons was measured after clamping of [Ca(2+)]i from 50 nM to 800 nM. Maximal ER Ca(2+) release was observed at approximately 200 nM [Ca(2+)]i, with noted blunting of release at higher [Ca(2+)]i. Steady-state mRNA transcript and protein levels revealed that the principal IP(3)R isoform expressed was IP(3)R-II. These results suggest that Ca(2+) loading in stellate ganglion neurons promotes Ang II-mediated decreases in [Ca(2+)]i via PKC and NO/cGMP/PKG pathways and inhibits IP(3)R-II-mediated ER Ca(2+) release.
Fernandez
Stanley F
SF
Department of Pharmacology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, USA.
Huang
Ming-He
MH
Davidson
Bruce A
BA
Knight
Paul R
PR
Izzo
Joseph L
JL
D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007425:Intracellular Membranes / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D009994:Osmolar Concentration; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013233:Stellate Ganglion / Q000166:cytology / Q000378:metabolism*; D010738:Type C Phospholipases / Q000502:physiology
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D000804:Angiotensin II; D009569:Nitric Oxide; D015544:Inositol 1,4,5-Trisphosphate; D011493:Protein Kinase C; D010738:Type C Phospholipases; D002118:Calcium