Electrogenic Ca2+ entry in the rat colonic epithelium

Capacitative Ca2+ entry in isolated rat colonic crypts was induced by dialy sing the cells in the whole-cell patch-clamp mode with a pipette solution h aving a high Ca2+-buffering capacity. Under these conditions crypt cell res ting potential was lower than normal. Flufenamate, La3+ and Gd3+, blockers of non-selective cation channels, hyperpolarized the crypt cells and decrea sed membrane current. This current exhibited a cation selectivity of Na+>Ca 2+. In contrast to Na+, Ca2+ inhibited the current at concentrations exceed ing 1 mmol/l. Indirect evidence suggests that the non-selective cation cond uctance is activated after stimulation of muscarinic receptors. Carbachol, a cholinergic agonist, evoked a transient hyperpolarization and an increase in membrane outwards current. The half-time of the decay of the carbachol response was shortened strongly in the presence of La3+ Fura-2 experiments with isolated crypts confirmed that La3+ inhibited: the carbachol-induced i ncrease in intracellular Ca2+. In Parallel Ussing chamber experiments, La3 suppressed the induction of Cl- secretion by carbachol. These-results demo nstrate that a non-selective cation conductance activated by store depletio n may be involved in the regulation of electrolyte transport by agonists of the Ca2+ signalling pathway.