Regulatory volume decrease (RVD) is a key mechanism for volume control that serves to prevent detrimental swelling in response to hypo-osmotic stress. The molecular basis of RVD is not understood. Here we show that a complex containing aquaporin-4 (AQP4) and transient receptor potential vanilloid 4 (TRPV4) is essential for RVD in astrocytes. Astrocytes from AQP4-KO mice and astrocytes treated with TRPV4 siRNA fail to respond to hypotonic stress by increased intracellular Ca 2+ and RVD. Coimmunoprecipitation and immunohistochemistry analyses show that AQP4 and TRPV4 interact and colocalize. Functional analysis of an astrocyte-derived cell line expressing TRPV4 but not AQP4 shows that RVD and intracellular Ca 2+ response can be reconstituted by transfection with AQP4 but not with aquaporin-1. Our data indicate that astrocytes contain a TRPV4/AQP4 complex that constitutes a key element in the brain's volume homeostasis by acting as an osmosensor that couples osmotic stress to downstream signaling cascades.water channel | glia | brain edema A basic property of any cell type is the ability to resist volume changes in the face of hypotonic stress. Thus, most cells are equipped with mechanisms that help bring cell volume back toward baseline level in the wake of an osmotically induced swelling response. This volume recovery, termed "regulatory volume decrease" (RVD) (1), plays a critical role in the brain, whose functional and structural integrity depends on finely tuned volume homeostasis at the cellular as well as the organ level.A wealth of data indicates that astroglial cells are essential for the maintenance of volume homeostasis in brain (2). Being equipped with AQP4 water channels in their foot processes at the interface between brain and liquid spaces, astrocytes are the first cells to be exposed to osmotic changes and the first cells to swell in response to hypo-osmotic stress (3-5). Further, the proximity of the astroglial processes to the subarachnoidal space and vessels (which act as sinks for excess osmolytes) places astroglia in a unique position for mediating regulatory volume changes, on the part of the astrocytic syncytium and the brain as a whole.A full mechanistic understanding of RVD would pave the way for more sophisticated measures to curtail pathological changes in brain water transport and distribution, as seen in brain tumors, stroke, and several other acute conditions that carry a high morbidity and lethality because of the loss of volume homeostasis. Future drugs affecting AQP4-mediated water transport would be expected to alleviate the acute consequences of inadvertent changes in osmotic driving forces. However, because the lipid bilayer of plasma membranes allows water diffusion (albeit to a restricted extent compared with membranes containing aquaporins), the long-term consequences of osmotic challenges can be offset only by manipulating the osmotic gradients per se. In this context, the RVD mechanisms stand out as targets of potential pharmacological interest (1, 6).Previous studies of t...

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The polymodal transient receptor potential vanilloid 4 (TRPV4) channel, a member of the TRP channel family, is a calcium-permeable cationic channel that is gated by various stimuli such as cell swelling, low pH and high temperature. Therefore, TRPV4-mediated calcium entry may be involved in neuronal and glia pathophysiology associated with various disorders of the central nervous system, such as ischemia. The TRPV4 channel has been recently found in adult rat cortical and hippocampal astrocytes; however, its role in astrocyte pathophysiology is still not defined. In the present study, we examined the impact of cerebral hypoxia/ischemia (H/I) on the functional expression of astrocytic TRPV4 channels in the adult rat hippocampal CA1 region employing immunohistochemical analyses, the patch-clamp technique and microfluorimetric intracellular calcium imaging on astrocytes in slices as well as on those isolated from sham-operated or ischemic hippocampi. Hypoxia/ischemia was induced by a bilateral 15-minute occlusion of the common carotids combined with hypoxic conditions. Our immunohistochemical analyses revealed that 7 days after H/I, the expression of TRPV4 is markedly enhanced in hippocampal astrocytes of the CA1 region and that the increasing TRPV4 expression coincides with the development of astrogliosis. Additionally, adult hippocampal astrocytes in slices or cultured hippocampal astrocytes respond to the TRPV4 activator 4-alpha-phorbol-12,-13-didecanoate (4αPDD) by an increase in intracellular calcium and the activation of a cationic current, both of which are abolished by the removal of extracellular calcium or exposure to TRP antagonists, such as Ruthenium Red or RN1734. Following hypoxic/ischemic injury, the responses of astrocytes to 4αPDD are significantly augmented. Collectively, we show that TRPV4 channels are involved in ischemia-induced calcium entry in reactive astrocytes and thus, might participate in the pathogenic mechanisms of astroglial reactivity following ischemic insult.

We present the integration of a natural protein into electronic and optoelectronic devices by using silk fibroin as a thin film dielectric in an organic thin film field-effect transistor (OFET) ad an organic light emitting transistor device (OLET) structures. Both n- (perylene) and p-type (thiophene) silk-based OFETs are demonstrated. The measured electrical characteristics are in agreement with high-efficiency standard organic transistors, namely charge mobility of the order of 10-2 cm2/Vs and on/off ratio of 104. The silk-based optolectronic element is an advanced unipolar n-type OLET that yields a light emission of 100nW.