Participation of cAMP in tacrine-induced gastric smooth muscle relaxation |
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Authors: | Natalia A Prissadova Mariana D Argirova Athanas D Krastev Valentin I Turiiski Rayna I Ardasheva |
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Institution: | (1) Department of Chemistry and Biochemistry, Medical University, 15a Vassil Aprilov Street, 4002 Plovdiv, Bulgaria;(2) Department of Biophysics, Medical University, 15a Vassil Aprilov Street, 4002 Plovdiv, Bulgaria |
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Abstract: | Tacrine, a well-known acetylcholinesterase inhibitor, applied in concentrations higher than 2×10−5 mol/l promoted Ca2+-independent relaxation of rat gastric smooth muscles in experiments in vitro. The relaxation was not cholinergic and was
a result of influence of tacrine over intracellular signaling pathways regulating smooth muscle contraction/relaxation. The
nature of this untypical muscle relaxation was studied by using smooth muscle strips isolated from rat stomach. Their bioelectrical
and mechanical responses were recorded after treatment with tacrine and different activators or blockers of intracellular
pathways involved in muscle contractility. Following the activation of adenylate cyclase with 1×10−6 mol/l forskolin and increase in the concentration of cyclic adenosine monophosphate (cAMP) after application of 4×10−5 mol/l SQ22536, a significant decrease in the muscle relaxation was observed. Theophylline (2×10−4 mol/l), a phosphodiesterase inhibitor, had no effect on the amplitude of tacrine-induced relaxation. The latter was also
reduced by inhibition of protein kinase A (PKA) with 5×10−6 mol/l KT5720. These findings support the assumption that tacrine promoted smooth muscle relaxation through PKA-induced phosphorylation
and inhibition of myosin light chain kinase activity. The reduction of spike-linked Ca2+ influx provoked by tacrine was probably a secondary contributing process, associated with an influence of increased cAMP
level on Ca2+ channels. |
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