Epithelial cell volume regulation: bicarbonate dependence.

When Necturus gallbladder epithelial cells are osmotically shrunken, they rapidly return to their original volume despite the continued presence of a hypertonic bathing solution. This volume-regulatory process requires bicarbonate ions in the bathing solutions and is associated with the uptake of chloride ions. Volume-regulatory increase by epithelial cells in probable due to the parallel operation of sodium-hydrogen and chloride-bicarbonate exchangers in the apical cell membrane.