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  • Title: Electrogenic Ca2+ entry in the rat colonic epithelium.
    Author: Frings M, Schultheiss G, Diener M.
    Journal: Pflugers Arch; 1999 Dec; 439(1-2):39-48. PubMed ID: 10650998.
    Abstract:
    Capacitative Ca2+ entry in isolated rat colonic crypts was induced by dialysing the cells in the whole-cell patch-clamp mode with a pipette solution having a high Ca(2+)-buffering capacity. Under these conditions crypt cell resting potential was lower than normal. Flufe-namate, La3+ and Gd3+, blockers of non-selective cation channels, hyperpolarized the crypt cells and decreased membrane current. This current exhibited a cation selectivity of Na+>Ca2+. In contrast to Na+, Ca(2+) inhibited the current at concentrations exceeding 1 mmol/l. Indirect evidence suggests that the non-selective cation conductance 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 increase in intracellular Ca2+. In parallel Ussing chamber experiments, La3+ suppressed the induction of Cl- secretion by carbachol. These results demonstrate that a non-selective cation conductance activated by store depletion may be involved in the regulation of electrolyte transport by agonists of the Ca2+ signalling pathway.
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