1. ¹Laboratoire de Biochimie et de Biologie Cellulaire, Institut de Pharmacie, Université libre de Bruxelles, B-1050 Brussels, Belgium
2. ²Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad del País Vasco, 48080 Bilbao, Spain

Correspondence: M Métioui, Laboratoire de Biochimie et de Biologie Cellulaire, Institut de Pharmacie C.P. 205/3, Université libre de Bruxelles, Boulevard du Triomphe, B-1050 Brussels, Belgium. E-mail: mmetioui@ulb.ac.be

Received 5 February 2002; Accepted 4 April 2002.

Abstract

1. The effect of trichloroethanol (TCEt), the active metabolite of chloral hydrate, on the intracellular concentration of calcium ([Ca²⁺]_i) was investigated in rat submandibular glands (RSMG) acini loaded with fura-2.
2. TCEt (1–10 mM) increased the [Ca²⁺]_i independently of the presence of calcium in the extracellular medium. Dichloroethanol (DCEt) and monochloroethanol (MCEt) reproduced the stimulatory effect of TCEt but at much higher concentrations (about 6 fold higher for DCEt and 20 fold higher for MCEt).
3. TCEt mobilized an intracellular pool of calcium, which was depleted by a pretreatment with thapsigargin, an inhibitor of the sarcoplasmic and endoplasmic reticulum calcium-dependent ATPases, but not with FCCP, an uncoupler of mitochondria.
4. TCEt 10 mM inhibited by 50% the thapsigargin-sensitive microsomal Ca²⁺-ATPase. DCEt 10 mM and MCEt 10 mM inhibited the ATPase by 20 and 10%, respectively.
5. TCEt inhibited the increase of the [Ca²⁺]_i and the production of inositol phosphates in response to carbachol, epinephrine and substance P.
6. TCEt inhibited the uptake of calcium mediated by the store-operated calcium channel (SOCC).
7. ATP and Bz-ATP increased the [Ca²⁺]_i in RSMG acini and this effect was blocked by extracellular magnesium, by Coomassie blue and by oxydized ATP (oATP).
8. TCEt potentiated the increase of the [Ca²⁺]_i and of the uptake of extracellular calcium in response to ATP and Bz-ATP.
9. TCEt had no effect on the uptake of barium and of ethidium bromide in response to purinergic agonists.
10. These results suggest that TCEt, at sedative concentrations, exerts various effects on the calcium regulation: (1) it mobilizes a thapsigargin-sensitive intracellular pool of calcium in RSMG acini; (2) it inhibits the uptake of calcium via the SOCC; (3) it inhibits the activation by G protein-coupled receptors of a polyphosphoinositide-specific phospholipase C. It does not interfere with the activation of the ionotropic P2X receptors.
11. The use of chloral hydrate should be avoided in studies exploring the in vivo responses to sialagogues.