1: J Exp Zool. 2003 Jun 1;297A(2):130-137.  
Effects of ionomycin and thapsigargin on ion currents in oocytes of Bufo arenarum.

Cavarra MS, Assef YA, Kotsias BA.

Instituto de Investigaciones Medicas Alfredo Lanari, Facultad de Medicina, UBA, Buenos Aires and Universidad Maimonides, Buenos Aires, Argentina.

In this study, two electrode voltage clamp technique was used to assess the ionic current of oocytes of the South American toad Bufo arenarum and to study the dependence of these currents on the extracellular and intracellular Ca(2+) concentrations. Ca(2+) chelators, ionomycin -a calcium ionophore- and thapsigargin, a blocker of the Ca(2+) pump of the sarcoplasmic reticulum, were used. The main results were the following: Most oocytes showed a voltage activated rectifying conductance. Ionomycin (1&mgr;M) increased inward and outward currents in control solution. The effect of ionomycin was blocked partially at negative potentials and was blocked completely at positive potentials in absence of extracellular Ca(2+). When the oocytes were treated with thapsigargin (2 &mgr;M) or BAPTA-am, a membrane-permeant intracellular chelator in control solution (10 &mgr;M), ionomycin did not increased either inward nor outward currents. The conclusion of our experiments is that there are two sources of Ca(2+) for activation of the current induced by ionomycin, the cytoplasmic stores and the extracellular space. We believe ionomycin directly translocates Ca(2+) from the SER into the cytoplasm but not from the extracellular medium. Ca(2+) entry probably occurs through store-operated-Ca-channels. J. Exp. Zool. 297A:130-137, 2003. Copyright 2003 Wiley-Liss, Inc.

PMID: 12783473 [PubMed - as supplied by publisher]




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