Identifying the Ca(++) signalling sources activating chloride currents in Xenopus oocytes using ionomycin and thapsigargin.
The calcium ionophore, ionomycin (IM), and the sarcoplasmic/endoplasmic reticulum (SER) calcium pump inhibitor, thapsigargin (TG), were used to study the roles of Ca(++) from different sources in regulating Ca(++)-dependent Cl(-) currents in Xenopus oocytes. The Ca(++)-dependent Cl(-) currents, Ic, were measured in voltage-clamped oocytes (Vc = -60 mV). In the presence of extracellular Ca(++), both TG (0.1 to 10 microM) and IM (0.1 to 10 microM) induce release of Ca(++) from SER and activated capacitative Ca(++) entry (CCE) across the plasma membrane leading to activation of both "fast" and "slow" Cl(-) currents. The fast Ic was produced by Ca(++) release from SER while Ca(++) entry across the plasma membrane activated the slow Ic. Intracellular application of the calcium buffer, BAPTA, blocked activation of the slow Ic due to Ca(++) entry via CCE pathways, but not via IM-mediated movement across the plasma membrane. It is concluded that predominantly Ca(++) release from stores regulates a fast Ic while Ca(++) entry through CCE pathways regulates a slow Ic. Further, the CCE and slow Ic pathways must be located in spatially separated compartments since BAPTA can effectively abolish the effects of Ca(++) entry via the CCE pathway, but not by the IM-mediated entry pathway.
Thurman
C L
CL
Department of Biology, University of Northern Iowa, Cedar Falls, IA 50614-0421, USA. Thurman@uni.edu
Burns
J S
JS
O'Neil
R G
RG
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism / Q000494:pharmacology; D020013:Calcium Signaling / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D015759:Ionomycin / Q000378:metabolism / Q000494:pharmacology; D007476:Ionophores / Q000378:metabolism / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D019284:Thapsigargin / Q000378:metabolism / Q000494:pharmacology; D014982:Xenopus laevis
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D018118:Chloride Channels; D007476:Ionophores; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D015759:Ionomycin; D019284:Thapsigargin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid