Evidence for agonist-induced export of intracellular Ca2+ in epithelial cells.
There is increasing evidence that some agonists not only induce intracellular Ca2+ increases, due to store release and transmembranous influx, but also that they stimulate Ca2+ efflux. We have investigated the agonist-stimulated response on the intracellular Ca2+ activity ([Ca2+]i) in the presence of thapsigargin (10(-8) mol/l, TG) in HT29 and CFPAC-1 cells. For CFPAC-1 the agonists ATP (10(-7)-10(-3) mol/l, n = 9), carbachol (10(-6)-10(-3) mol/l, n = 5) and neurotensin (10(-10)-10(-7) mol/l, n = 6) all induced a concentration-dependent decrease in [Ca2+]i in the presence of TG. Similar results were obtained with HT29 cells. This decrease of [Ca2+]i could be caused by a reduced Ca2+ influx, either due to a reduced driving force for Ca2+ in the presence of depolarizing agonists or due to agonist-regulated decrease in Ca2+ permeability. Using the fura-2 Mn2+ quenching technique we demonstrated that ATP did not slow the TG-induced Mn2+ quench. This indicates that the agonist-induced [Ca2+]i decrease in the presence of TG was not due to a reduced influx of Ca2+ into the cell, but rather due to stimulation of Ca2+ export. We used the cell attached nystatin patch clamp technique in CFPAC-1 cells to examine whether, in the presence of TG, the above agonists still led to the previously described electrical changes. The cells had a mean membrane voltage of -49 +/- 3.6 mV (n = 9). Within the first 3 min ATP was still able to induce a depolarization which could be attributed to an increase in Cl- conductance.(ABSTRACT TRUNCATED AT 250 WORDS)
Wolff
T
T
Physiologisches Institut, Albert-Ludwigs-Universität, Freiburg, Germany.
Leipziger
J
J
Fischer
K G
KG
Klär
B
B
Nitschke
R
R
Greger
R
R
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D008345:Manganese / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014638:Vanadates / Q000494:pharmacology
D013729:Terpenes; D014638:Vanadates; D008345:Manganese; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D002217:Carbachol; D012964:Sodium; D002118:Calcium