Interaction between store-operated non-selective cation channels and the Na(+)-Ca(2+) exchanger during secretion in the rat colon.
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.
Seip
G
G
Institut für Veterinär-Physiologie, Justus-Liebig-Universität Giessen, D-35392 Giessen, Germany.
Schultheiss
G
G
Kocks
S L
SL
Diener
M
M
D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000493:pharmacokinetics; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000493:pharmacokinetics; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D018678:Cholinergic Agents / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D008274:Magnesium / Q000493:pharmacokinetics; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000493:pharmacokinetics; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000493:pharmacokinetics; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013324:Strontium / Q000493:pharmacokinetics
D002412:Cations; D018678:Cholinergic Agents; D007473:Ion Channels; D019831:Sodium-Calcium Exchanger; C041470:3',4'-dichlorobenzamil; D001464:Barium; D000584:Amiloride; D002217:Carbachol; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium; D013324:Strontium