Ammonium increases Ca2+ signalling and upregulates expression of Cav1.2 gene in astrocytes in primary cultures and in the in vivo brain. (18th April 2015)

• Record Type: Journal Article
• Authors: Wang, F.; Du, T.; Liang, C.; Verkhratsky, A.; Peng, L.
• Is Part Of: Acta physiologica. Volume 214:Number 2(2015:Jun.)
• Page Start: 261
• Page End: 274
• Publication Date: 2015-04-18
• Subjects: Physiology -- Periodicals; Physiology -- Research -- Periodicals; 612
• DOI: 10.1111/apha.12500
• Languages: English
• ISSNs: 1748-1708

Abstract

<abstract abstract-type="main" id="apha12500-abs-0001"> <title>Abstract</title> <sec id="apha12500-sec-0001" sec-type="section"> <title>Aim</title> <p>The primary aim of this study was to identify the effects of hyperammonaemia on functional expression of Ca<sub>v</sub>1.2 L‐type Ca<sup>2+</sup> channels in astroglia.</p> </sec> <sec id="apha12500-sec-0002" sec-type="section"> <title>Methods</title> <p>Primary cultures of mouse astrocytes were used to study effects of chronic treatment (1–5 days) with ammonium chloride, at 1, 3 and 5 m<sc>m</sc> on depolarization‐induced increases in free cytosolic Ca<sup>2+</sup> concentration ([Ca<sup>2+</sup>]<sub>i</sub>, measured with Fura‐2 based microfluorimetry) in control conditions and following treatment with the L‐type Ca<sup>2+</sup> channel inhibitor, nifedipine, or with ryanodine receptor inhibitor, ryanodine. Expression of Ca<sub>v</sub>1.2 mRNA was identified with RT‐PCR, whereas protein content was determined by Western blotting. Sustained hyperammonaemia <italic>in vivo</italic> was induced by daily injections of urease (33 units kg body weight<sup>−1</sup>, i.p.) for 3 days.</p> </sec> <sec id="apha12500-sec-0003" sec-type="section"> <title>Results</title> <p>Depolarization‐induced [Ca<sup>2+</sup>]<sub>i</sub> transients sensitive to nifedipine (peak of the response) and to ryanodine (plateau phase) were significantly increased in astrocytes chronically exposed to ammonium. The ammonium‐induced increase in Ca<sup>2+</sup> influx in astrocytes resulted from an upregulation of Ca<sub>v</sub>1.2 channel's expression detected at mRNA and protein levels. Increase in Ca<sub>v</sub>1.2 expression was prevented by ouabain antagonist canrenone. Similar upregulation of Ca<sub>v</sub>1.2 gene expression was found in the brains of adult mice subjected to intraperitoneal injection of urease. In transgenic mice tagged with an astrocyte‐specific or neurone‐specific markers and treated with intraperitoneal injections of urease, the fluorescence‐activated cell sorting of neurones and astrocytes demonstrated that Ca<sub>v</sub>1.2 mRNA expression was upregulated in astrocytes, but not in neurones.</p> </sec> <sec id="apha12500-sec-0004" sec-type="section"> <title>Conclusions</title> <p>Ammonium‐induced deregulation of astroglial Ca<sup>2+</sup> signalling, is, in part, associated with upregulation of Ca<sub>v</sub>1.2 L‐type calcium channels.</p> </sec> </abstract>