|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
PMID: 12783473 [PubMed - as supplied by publisher]