Successful incorporation of short-interfering RNA into islet cells by in situ perfusion

Islet transplantation offers a potential cure for type I diabetes, although its success has been limited, due to loss of cells by apoptosis stimulated by the procurement, ischemia, and the isolation process itself. RNA interference (RNAi) as mediated by short interfering RNAs (siRNAs) has become a potent tool to manipulate gene expression in mammalian cells. We describe the first successful introduction of siRNA directly into pancreatic islet cells both during in situ perfusion and from intravenous tail vein injection (in vivo).

METHODS

siRNA was targeted to the pancreatic islets of BALB/c mice by retrograde portal vein perfusion or tail vein injection. Cy3-labeled siRNA was dissolved in University of Wisconsin (UW) solution at 2 microg/mL. After delivery pancreata were placed in cold storage at 4 degrees C in UW solution for 24 hours, followed by processing for immunofluorescent staining for insulin. Fluorescent imaging was obtained using a Nikon DIAPHOT 300 Inverted Micoscope with a Zeiss AxioCam and OpenLab image capturing software.

RESULTS

In situ delivery of siRNA was demonstrated by fluorescent imaging composites of (red) siRNA in and along (green) insulin stained islets from pancreas sections as compared with untreated control sections. The siRNA was detected mainly in and along venous structures throughout the pancreatic tissue. In vivo delivery of siRNA into islets was observed by fluorescent images taken of isolated islets in culture.

CONCLUSIONS

We have described the successful delivery of siRNA to pancreatic islets via a novel in situ pancreas perfusion technique and in vivo delivery via tail vein injection.

Biphasic modulation of the strychnine-sensitive glycine receptor by Zn2+

The effects of extracellular applications of Zn2+ ions on the strychnine-sensitive glycine receptor were studied in cultured rat spinal cord neurons and with recombinant glycine receptors expressed in human embryonic kidney 293 cells. Nanomolar concentrations of Zn2+ enhanced the chloride ion current in response to brief applications of 100 microM glycine. The enhancement of glycine responses increased from 20 nM to 1 microM Zn2+. Higher concentrations of Zn2+ caused a reversal of the potentiation, followed by progressive inhibition of the glycine response up to approximately 20-50 microM Zn2+. The biphasic modulation by Zn2+ appeared essentially identical in native and recombinant glycine receptors. Biphasic Zn2+ modulation was observed both with picrotoxin-insensitive heteromeric (alpha 2/beta) receptors and with picrotoxin-sensitive homomeric receptors consisting only of alpha 2 subunits. This suggests that the alpha subunit alone is sufficient for formation of two distinct Zn2+ binding sites on the glycine receptor. The demonstration of Zn2+ modulation of the strychnine-sensitive glycine receptor is of potential physiological importance, in view of the likely range of subsynaptic Zn2+ concentrations to which the receptor is exposed.