Details

Autor(en) / Beteiligte

• Vedovato, N
• Rispoli, G

Titel

Modulation of the reaction cycle of the Na super(+): Ca super(2+), K super(+) exchanger

Ist Teil von

• European biophysics journal, 2007-09, Vol.36 (7), p.787-793

Erscheinungsjahr

2007

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Ca super(2+) concentration in retinal photoreceptor rod outer segment (OS) strongly affects the generator potential kinetics and the receptor light adaptation. The response to intense light stimuli delivered in the dark produce potential changes exceeding 40 mV: since the Ca super(2+) extrusion in the OS is entirely controlled by the Na super(+): Ca super(2+), K super(+) exchanger, it is important to assess how the exchanger ion transport rate is affected by the voltage and, in general, by intracellular factors. It is indeed known that the cardiac Na super(+): Ca super(2+) exchanger is regulated by Mg-ATP via a still unknown metabolic pathway. In the present work, the Na super(+): Ca super(2+), K super(+) exchanger regulation was investigated in isolated OS, recorded in whole-cell configuration, using ionic conditions that activated maximally the exchanger in both forward and reverse mode. In all species examined (amphibia: Rana esculenta and Ambystoma mexicanum; reptilia: Gecko gecko), the forward (reverse) exchange current increased about linearly for negative (positive) voltages and exhibited outward (inward) rectification for positive (negative) voltages. Since hyperpolarisation increases Ca super(2+) extrusion rate, the recovery of the dark level of Ca super(2+) (and, in turn, of the generator potential) after intense light stimuli results accelerated. Mg-ATP increased the size of forward and reverse exchange current by a factor of -2.3 and -2.6, respectively, without modifying their voltage dependence. This indicates that Mg-ATP regulates the number of active exchanger sites and/or the exchanger turnover number, although via an unknown mechanism.