Characterization of a membrane potassium ion conductance in intestinal secretory cells using whole cell patch-clamp and calcium ion-sensitive dye techniques

This chapter describes a strategy for characterizing the changes in membrane K ⁺ conductance that result from exposure of isolated cells of the human secretory cell line T84 to a cholinergic agonist, and the role of intracellular Ca ²⁺ as a mediator of that process. These findings in isolated T84 cells are consistent with the proposed model for muscarinic agonist-induced Cl^- secretion by an epithelium, in which an agonist-induced increase in basolateral membrane K ⁺ conductance hyperpolarizes the cells and causes secretion by increasing the driving force for C1^- exit across the apical membrane. Care must be used in interpretation of results from dialyzed cells. This is illustrated in the studies by the difference seen between the duration of the carbachol-induced K ⁺ current oscillations and Ca ²⁺ oscillations. In every cell studied, the K ⁺ current returned to baseline in the continued presence of carbachol.