Electrogenic Ca2+ entry in the rat colonic epithelium.
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.
Frings
M
M
Institut für Veterinär-Physiologie, Justus-Liebig-Universität Giessen, Germany.
Schultheiss
G
G
Diener
M
M
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D004594:Electrophysiology; D004847:Epithelial Cells / Q000378:metabolism; D005439:Flufenamic Acid / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D005682:Gadolinium / Q000494:pharmacology; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007811:Lanthanum / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018721:Muscarinic Agonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D013256:Steroids
D000893:Anti-Inflammatory Agents; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D005456:Fluorescent Dyes; D018721:Muscarinic Agonists; D013256:Steroids; D005439:Flufenamic Acid; D007811:Lanthanum; D002217:Carbachol; D012964:Sodium; D005682:Gadolinium; D016257:Fura-2