Interaction between store-operated non-selective cation channels and the Na(+)-Ca(2+) exchanger during secretion in the rat colon

• Published in: Experimental physiology Vol. 86; no. 4; pp. 461 - 468
• Main Authors: Seip, G, Schultheiss, G, Kocks, S L, Diener, M
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01.07.2001
• Subjects: Amiloride - analogs & derivatives; Amiloride - pharmacology; Animals; Barium - pharmacokinetics; Biological Transport - drug effects; Biological Transport - physiology; Calcium - pharmacokinetics; Carbachol - pharmacology; Cations - metabolism; Cholinergic Agents - pharmacology; Colon - metabolism; Colon - secretion; Homeostasis - physiology; Intestinal Mucosa - metabolism; Intestinal Mucosa - secretion; Ion Channels - metabolism; Magnesium - pharmacokinetics; Patch-Clamp Techniques; Potassium - pharmacokinetics; Rats; Rats, Wistar; Sodium - pharmacokinetics; Sodium-Calcium Exchanger - metabolism; Strontium - pharmacokinetics
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/eph8602243

The properties of capacitative Ca(2+) influx were studied using the whole-cell patch-clamp technique in crypts isolated from rat distal colon. Store-operated cation influx was evoked by increasing the intracellular buffering capacity for Ca(2+) in the pipette solution; contamination by Cl(-) currents was reduced by the use of NMDG gluconate as the main electrolyte in the pipette solution. The permeability of the non-selective cation conductance stimulated by store depletion had the following sequence for monovalent cations: Cs(+) > Na(+) > or = Li(+). The store-operated conductance is permeable to Na(+) and Ca(2+), but in contrast to Na(+), Ca(2+) also exerts a (feedback) inhibition on its own influx. Other divalent cations shared this inhibitory action with the sequence: Ca(2+) > or = Mg(2+) > or = Ba(2+) > or = Sr(2+). Fura-2 experiments revealed that replacement of extracellular Na(+) by NMDG(+) induced an increase in the intracellular Ca(2+) concentration, which was suppressed by the Na(+)-Ca(2+) exchange inhibitor, dichlorobenzamil, indicating the presence of a Na(+)-Ca(2+) exchanger within the colonic crypt cells. In Ussing chamber experiments dichlorobenzamil induced an increase in short-circuit current (I(sc)) in the majority of tissues tested indicating that this exchanger acts as a Ca(2+)-extruding transporter under physiological conditions. When Ca(2+)-dependent anion secretion was stimulated by the acetylcholine analogue carbachol, dichlorobenzamil no longer evoked an increase in I(sc), indicating that after stimulation of the store-operated cation conductance the Na(+)-Ca(2+) exchanger is turned off. Therefore, it is concluded that the influx of Na(+) across the non-selective store-operated cation conductance serves to reduce the driving force for Ca(2+) extrusion via the Na(+)-Ca(2+) exchanger and thereby maintains the increase in the intracellular Ca(2+) concentration during induction of secretion. Experimental Physiology (2001) 86.4, 461-468.