Xenopus laevis oocytes codify a G-protein-activated inward rectifier potassium channel (GIRK5 or Kir3.5). Coinjection of other GIRKs, the muscarinic m2 receptor, or Gbetagamma protein cRNAs is required to observe functional GIRKx-GIRK5 heteromultimers in oocytes. Studies with GIRK2 isoforms have shown that the size of the amino or carboxyl terminus plays a crucial role on giving functional K(+) channels. In this work we studied the properties of a GIRK5 with 25 amino acids deleted toward its amino-terminal domain. Injection of GIRK5-Delta25 cRNA alone displayed large basal and transient inward rectifying currents in oocytes. The instantaneous currents reached a stationary level after a long duration voltage pulse (10 s). For this relaxation, fast (tau(1)) and slow (tau(2)) time constants were estimated at different voltages. Recovery from inactivation followed a monoexponential function (tau=0.95+/-0.07 s). By contrast with other inward rectifier channels, blockade of GIRK5-Delta25 by extracellular Ba(2+) was voltage-independent (K(d)=102+/-2 microM), suggesting the presence of a Ba(2+) site at the external channel vestibule. To confirm this hypothesis, the Ba(2+) sensitivity of two charged mutants GIRK5-Delta25(N129E) and GIRK5-Delta25(K157E) at each of the external loops was determined. GIRK5-Delta25(N129E) and GIRK5-Delta25(K157E) showed a 100-fold and 2-fold higher affinity to Ba(2+), respectively, supporting the existence of this Ba(2+) binding site.

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Stimulation of the localized surface plasmon of metallic nanoparticles has been shown to be an effective mechanism to induce photothermal damage in biological tissues. However, few studies have focused on single cell or subcellular ablation. Our results show that, upon incubation, gold nanostars are internalized by neurons of acute mouse cerebellar brain slices, clustering inside or close to the nucleus. By stimulating the nanostars' surface plasmon using a femtosecond laser, we show deformation of single nuclei and single cells. Given its precision and extremely localized effect, this is a promising technique for photothermal therapy in areas sensitive to collateral thermal damage such as the nervous system. 409-453 (2000). 30. S. Link, C. Burda, B. Nikoobakht, and M. A. El-Sayed, "Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses," J.