Characterization of calcium sources and downstream signaling pathways following electrical field stimulation of rodent longitudinal esophageal muscle.

AIMS: To explore the mechanisms involved in esophageal body longitudinal muscle contraction induced by electrical field stimulation. METHODS: Isometric contractions of esophageal segments from wistar rats in an organ bath were induced by electrical field stimulation (duration 1 s, frequency 1-100 Hz, intensity 30-90 V) before and after application of pharmacological probes to test involvement of muscarinic receptors, Rho kinase, Ca2+ release, protein kinase C, calmodulin and L-type Ca2+ channels. RESULTS: Electrical field stimulation (EFS) induced contractions showed a frequency and intensity-dependent behavior. Based on the effect size, expressed by the Cohen's d, they were insensitive to the muscarinic receptor blocker atropine (1 µM), the Rho kinase inhibitor Y-27632 (10 µM) as well as the inhibitors of Ca2+ release 2-aminoethoxydiphenylborane (2-APB, 100µM) and 1,1'-diheptyl-4,4'-bipyridinium (DHBP, 100 µM). In contrast, contractions were reduced by the protein kinase C inhibitor chelerythrine (10µM) and by the calmodulin antagonist N-[6-aminohexyl]-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7, 100 µM). Verapamil (100 µM) abolished EFS-induced contractions. CONCLUSIONS: Based on our findings with 2-APB, DHBP, and verapamil, extracellular Ca²+ appears to be the source of the increase in intracellular Ca²+ underlying EFS-induced EB contractions. Furthermore, the effects observed with chelerythrine and W-7 may suggest that this increase in intracellular Ca²+ may subsequently activate PKC- and calmodulin-dependent signaling pathways.