Ba2+ selectively inhibits receptor-mediated contraction of the esophageal muscularis mucosae

The aim of the present study was to examine the effect of Ba2+ on acetylcholine- and KCl-induced contractions of the guinea-pig esophageal muscularis mucosae. When the muscularis mucosae was pretreated with nicardipine (1 microM), Ba2+ (0.1-30 mM) markedly inhibited the acetylcholine (3 microM)-induced tone, and at 10-30 mM the tone returned to its basal level. In contrast, Ba2+ (0.1-30 mM) slightly increased the KCl (60 mM)-induced tone. Moreover, the Ba2+ (30 mM)-increased KCl tone was completely inhibited by treatment with nicardipine (0.3-1 microM). In conclusion, Ba2+ both selectively inhibits receptor-mediated contraction of the muscularis mucosae and itself permeates through voltage-dependent Ca2+ channels.