Regional adrenergic regulation of ion transport across the isolated porcine gallbladder

The regional transport properties of the porcine gallbladder epithelium were studied using Ussing chambers in which tissues were bathed in porcine Ringer solution. Under basal conditions, tissues from the neck absorbed Na and Cl. Fundic tissues also absorbed Na, but net Cl transport was not different from zero. Serosal norepinephrine (NE; 0.1 μM) stimulated Na and Cl absorption in the neck but only Cl absorption in the fundus. The effects of NE on Na and Cl transport were blocked by pretreatment with yohimbine, suggesting that α₂-adrenoceptors mediate the transport-related actions of this neurotransmitter. Serosal isoproterenol (0.1 μM) produced a tetrodotoxin-insensitive, propranolol-sensitive increase in the short- circuit current (I(sc)) in fundic tissues but not in tissues from the neck. The β₂-adrenergic agonist salbutamol produced a response similar to that of isoproterenol. However, the β₁-adrenergic agonist dobutamine had no effect. Isoproterenol was 5.8-fold more potent than salbutamol in increasing the I(sc). A possible explanation for the regional effects of β-agonists is that β-adrenoceptors are localized to epithelial cells in the fundic region. These results and results obtained previously suggest regional differences in basal Na and Cl transport across the porcine gallbladder epithelium and that both α₂- and β₂-adrenoceptors act to regulate ion transport in this tissue.