The effects of carbachol on water and electrolyte fluxes and transepithelial electrical potential differences of the rabbit submaxillary main duct perfusedin vitro

Summary

The effect of carbachol on transepithelial potential difference and transepithelial nett electrolyte transport has been studied in the rabbit submaxillary main duct perfusedin vivo andin vitro with bicarbonate saline. The two preparations function similarly, reabsorbing Na, Cl and water and secreting K. In control ducts nett Na reabsorption was 683±55 nmol · cm⁻² · min⁻¹ and K secretion was 31.2±2.4 nmol · cm⁻² · min⁻¹. Nett water reabsorption was 970±71 nl · cm⁻² · min⁻¹ and the hydraulic conductivity was (14.0±1.6)×10⁻⁶ ml · cm⁻² · s⁻¹ · atm⁻¹. The mean transepithelial potential difference was 13.1±0.8 mV (lumen negative) and, assuming no active transport of Cl, the partial conductance of the duct to Cl was (12.7±2.6)×10⁻² mho · cm⁻². Carbachol,in vivo andin vitro, caused partial depolarization of the transepithelial potential difference and reduction of nett Na and Cl reabsorption. It was without effect on duct K and HCO₃ transport.In vitro, the drug was effective in concentrations as low as 10⁻⁷ M and perhaps lower. Atropine was able completely to block the effects of carbachol present at twice the atropine concentration. The results are consistent with the hypothesis that carbachol acts in some way to reduce the sodium conductance of the luminal face of the duct epithelial cell, this response being secondary to an undefined primary action of carbachol on the interstitial face of the cell.