Published online Feb 28, 2018. doi: 10.3748/wjg.v24.i8.882
Peer-review started: October 23, 2017
First decision: November 8, 2017
Revised: November 14, 2017
Accepted: November 28, 2017
Article in press: November 28, 2017
Published online: February 28, 2018
To investigate the signaling pathways involved in the relaxin (RLX) effects on ileal preparations from mice through mechanical and electrophysiological experiments.
For mechanical experiments, ileal preparations from female mice were mounted in organ baths containing Krebs-Henseleit solution. The mechanical activity was recorded via force-displacement transducers, which were coupled to a polygraph for continuous recording of isometric tension. Electrophysiological measurements were performed in current- and voltage-clamp conditions by a microelectrode inserted in a single smooth muscle cell (SMC) of the ileal longitudinal layer. Both the membrane passive properties and inward voltage-dependent L-type Ca2+ currents were recorded using suitable solutions and voltage stimulation protocols.
Mechanical experiments showed that RLX induced a decay of the basal tension and a reduction in amplitude of the spontaneous contractions. The effects of RLX were partially reduced by 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (ODQ) or 9-cyclopentyladenine mesylate (9CPA), inhibitors of guanylate cyclase (GC) and adenylate cyclase (AC), respectively, and were abolished in the concomitant presence of both drugs. Electrophysiological experiments demonstrated that RLX directly influenced the biophysical properties of ileal SMCs, decreasing the membrane conductance, hyperpolarizing the resting membrane potential, reducing the L-type calcium current amplitude and affecting its kinetics. The voltage dependence of the current activation and inactivation time constant was significantly speeded by RLX. Each electrophysiological effect of RLX was reduced by ODQ or 9CPA, and abolished in the concomitant presence of both drugs as observed in mechanical experiments.
Our new findings demonstrate that RLX influences ileal muscle through a dual mechanism involving both GC and AC.
Core tip: Up to now relaxin (RLX) was described to act only through the NO/guanylate cyclase (GC)/cGMP/PKG pathway in different gastrointestinal tracts. The results of the present study, achieved on mice ileal preparations and carried out by a combined mechanical and electrophysiological approach, demonstrate for the first time that both GC and adenylate cyclase are involved in the effects of RLX in this intestinal region. The activation of this dual signaling pathway by RLX might represent a reinforcing (redundant) myorelaxant mechanism in the ileum, underlying the physiological importance of the hormone and leading to speculate translational perspectives in the treatment of intestinal dysmotilities.