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Properties of the Ca(2+)-activated Cl- current of Xenopus oocytes
No full textThe properties of the Ca(2+)-activated Cl- current of Xenopus oocytes have been investigated by voltage-clamp and injections of D-3-deoxy-3-fluoro-myo-inositol 1,4,5-trisphosphate (3-F-lnsP3). Following 3-F-InsP3 injection, a transient phase of Ca(2+)-activated Cl- current occurred, caused by Ca2+ release from internal stores; subsequently, a secondary, long-lasting, current was recorded, signaling Ca2+ influx from the exterior (ICRAC). Changes in external Cl- during the sustained phase produced the expected shifts in reversal potential (Erev), while the conductance varied opposite to the predictions of simple electrodiffusional theory. Application of depolarizing pulses soon (10 s) after 3-F-InsP3 injection elicited membrane currents exhibiting a single exponential rise. During the sustained subsequent phase, the current elicited by depolarizations showed an early peak followed by a prominent decline. During the sustained phase, removal of calcium from the external solution, or its substitution with Ba2-, abolished voltage- and time-dependent components of the depolarization-induced current. Slope conductance analysis of the inactivating records revealed, in addition to the decline of the Ca(2+)-activated Cl- current, the presence of a second, inwardly directed current. This could be identified as a slowly inducible Na+ current already described in Xenopus oocytes
Interazione diretta tra il canale del calcio cardiaco di tipo L e la subunità a della proteina Gs
No full text
Ca2+-dependence of the depolarization-inducible Na+ current of Xenopus oocytes
No full textThe role of Ca2+ on the depolarization-induced appearance of a Na+ current in Xenopus oocytes was studied. Oocytes were voltage-clamped and the induction of the Na+ current was tested under various conditions. In oocytes pre-injected with 400 pmol EGTA to increase the intracellular Ca2+ buffering power, the current was significantly reduced. Conversely, when intracellular Ca2+ was made to increase by injecting an analogue of inositol 1,4,5-trisphosphate (3-F InsP3), to cause Ca2+ release from internal stores, the induction of the Na+ current was potentiated. The depolarization-inducible Na+ channels of the Xenopus oocyte membrane appear, therefore, to be Ca2+ sensitive, as well as depolarization-activated
Indications of a direct interaction between L-type Ca2+ channels and Gsa subunits revealed by antisense oligonucleotides in Xenopus oocytes
No full textPore-like behaviour of the lepidopteran amino acid transporter kaat1 expressed in xenopus oocytes
No full textIndications of a direct interaction between L-type Ca2+ channels and Gs alpha-subunits, revealed by antisense oligonucleotides in Xenopus oocytes
No full textIon binding and permeation through the lepidopteran amino acid transporter KAAT1 expressed in Xenopus oocytes
No full textThe transient and steady-state currents induced by voltage jumps in Xenopus oocytes expressing the lepidopteran amino acid co-transporter KAAT1 have been investigated by two-electrode voltage clamp. 2. KAAT1-expressing oocytes exhibited membrane currents larger than controls even in the absence of amino acid substrate (uncoupled current). The selectivity order of this uncoupled current was Li+ > Na+ approximately Rb+ approximately K+ > Cs+; in contrast, the permeability order in non-injected oocytes was Rb+ > K+ > Cs+ > Na+ > Li+. 3. KAAT1-expressing oocytes gave rise to 'pre-steady-state currents' in the absence of amino acid. The characteristics of the charge movement differed according to the bathing ion: the curves in K+ were strongly shifted (> 100 mV) towards more negative potentials compared with those in Na+, while in tetramethylammonium (TMA+) no charge movement was detected. 4. The charge-voltage (Q-V) relationship in Na+ could be fitted by a Boltzmann equation having V of -69 +/- 1 mV and slope factor of 26 +/- 1 mV; lowering the Na+ concentrations shifted the Q-V relationship to more negative potentials; the curves could be described by a generalized Hill equation with a coefficient of 1.6, suggesting two binding sites. The maximal movable charge (Qmax) in Na+, 3 days after injection, was in the range 2.5-10 nC. 5. Addition of the transported substrate leucine increased the steady-state carrier current, the increase being larger in high K+ compared with high Na+ solution; in these conditions the charge movement disappeared. 6. Applying Eyring rate theory, the energy profile of the transporter in the absence of organic substrate included a very high external energy barrier (25.8 RT units) followed by a rather deep well (1.8 RT units)
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