Angiotensin II regulation of intracellular calcium in astroglia cultured from rat hypothalamus and brainstem.
This study examines the angiotensin II (Ang II) regulation of intracellular free calcium concentration ([Ca2+]i) in astroglia cultured from the hypothalamus and brainstem of the adult rat. Bath perfusion or rapid puffer application of angiotensin II (Ang II) (1-100 nM) increased [Ca2+]i in both polygonal and stellate astroglia when measured using fura-2 imaging fluorescence microscopy. Ang II increased [Ca2+]i in 96.1 and 95.6% of the polygonal and stellate glial cells, respectively. In normal Tyrode's solution (containing 2 mM CaCl2), the Ang II-stimulated increase in [Ca2+]i characteristically showed a biphasic response, i.e., an initial rapid transient peak followed by a sustained, steady-state plateau of free Ca2+. In both cell types, the selective Ang II type 1 receptor subtype (AT1) antagonist losartan (1 microM) inhibited the Ang II-stimulated increase in [Ca2+]i. The selective AT2 antagonist PD 123319 (1 microM) did not inhibit the Ang II-stimulated increase in [Ca2+]i in either cell type. To define the sources of Ca2+ that participate in the Ang II-stimulated increase in [Ca2+]i in astroglia, experiments were performed in a nominally Ca(2+)-free Tyrode's solution. In either cell type, this resulted in only an initial transient increase of Ca2+ and no sustained plateau of Ca2+ when challenged with Ang II. Thapsigargin (5 microM), cyclopiazonic acid (10 microM), and ryanodine (10 microM), but not caffeine (1-10 mM), inhibited the initial rise in [Ca2+]i. The plateau increase of [Ca2+]i caused by Ang II (100 nM) was reversibly inhibited by both cadmium (100 microM) and nifedipine (10 microM); in contrast, gadolinium (100 microM) had no effect on the plateau increase of [Ca2+]i. These results indicate that Ang II, in physiological concentrations, can activate AT1 receptors to stimulate both Ca2+ release from intracellular stores and Ca2+ influx from the extracellular space to increase [Ca2+]i of polygonal and stellate astroglia.
Wang
D
D
Department of Physiology, University of Florida College of Medicine, Gainesville 32610, USA.
Martens
J R
JR
Posner
P
P
Sumners
C
C
Gelband
C H
CH
D000804:Angiotensin II / Q000494:pharmacology*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001253:Astrocytes / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D001713:Biphenyl Compounds / Q000494:pharmacology; D001933:Brain Stem / Q000166:cytology*; D002104:Cadmium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005682:Gadolinium / Q000494:pharmacology; D007031:Hypothalamus / Q000166:cytology*; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D019808:Losartan; D009543:Nifedipine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011945:Receptors, Angiotensin / Q000737:chemistry / Q000502:physiology; D012433:Ryanodine / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology; D013777:Tetrazoles / Q000494:pharmacology; D019284:Thapsigargin; D013997:Time Factors
D057911:Angiotensin Receptor Antagonists; D001713:Biphenyl Compounds; D002121:Calcium Channel Blockers; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007211:Indoles; D010726:Phosphodiesterase Inhibitors; D011725:Pyridines; D011945:Receptors, Angiotensin; D013729:Terpenes; D013777:Tetrazoles; D002104:Cadmium; D000804:Angiotensin II; C073402:PD 123319; D012433:Ryanodine; D002110:Caffeine; D019284:Thapsigargin; D005682:Gadolinium; D009543:Nifedipine; D019808:Losartan; D002118:Calcium; C000543:cyclopiazonic acid