The sensation of pressure, mechanosensation, in vertebrates remains poorly understood on the molecular level. The ion channel TRPV4 is in the TRP family and is a candidate for a mechanosensitive calcium-permeable channel. It is located in dorsal root ganglia. In the present study, we show that disrupting the Trpv4 gene in mice markedly reduced the sensitivity of the tail to pressure and acidic nociception. The threshold to noxious stimuli and the conduction velocity of myelinated nerve responding to stimuli were also impaired. Activation of unmyelinated nerve was undetected. However, the mouse still retained olfaction, taste sensation, and heat avoidance. The TRPV4 channel expressed in vitro in Chinese hamster ovary cells was opened by low pH, citrate, and inflation but not by heat or capsaicin. These data identify the TRPV4 channel as essential for the normal detection of pressure and as a receptor of the high-threshold mechanosensory complex.

Claudin-2 is highly expressed in tight junctions of mouse renal proximal tubules, which possess a leaky epithelium whose unique permeability properties underlie their high rate of NaCl reabsorption. To investigate the role of claudin-2 in paracellular NaCl transport in this nephron segment, we generated knockout mice lacking claudin-2 (Cldn2 −/− ). The Cldn2 −/− mice displayed normal appearance, activity, growth, and behavior. Light microscopy revealed no gross histological abnormalities in the Cldn2 −/− kidney. Ultrathin section and freezefracture replica electron microscopy revealed that, similar to those of wild types, the proximal tubules of Cldn2 −/− mice were characterized by poorly developed tight junctions with one or two continuous tight junction strands. In contrast, studies in isolated, perfused S2 segments of proximal tubules showed that net transepithelial reabsorption of Na + , Cl -, and water was significantly decreased in Cldn2 −/− mice and that there was an increase in paracellular shunt resistance without affecting the apical or basolateral membrane resistances. Moreover, deletion of claudin-2 caused a loss of cation (Na + ) selectivity and therefore relative anion (Cl -) selectivity in the proximal tubule paracellular pathway. With free access to water and food, fractional Na + and Cl -excretions in Cldn2 −/− mice were similar to those in wild types, but both were greater in Cldn2 −/− mice after i.v. administration of 2% NaCl. We conclude that claudin-2 constitutes leaky and cation (Na + )-selective paracellular channels within tight junctions of mouse proximal tubules. mouse proximal tubule | tight junction | paracellular transport | Na/Cl transport | water transport T ight junctions (TJs) are circumferential seals around cells that selectively modulate paracellular permeability between extracellular compartments (1-3). On ultrathin-section electron microscopy, TJs appear as foci where the plasma membranes of neighboring cells make complete contact (4). On freeze-fracture electron microscopy, TJs appear as a continuous and anastomosing network of intramembranous particle strands (TJ strands) (5). These strands are mainly composed of linearly polymerized integral membrane proteins called claudins with molecular masses of ∼23 kDa (2, 3, 6). The claudin gene family contains more than 20 members in humans and in mice (2, 3, 7). The expression pattern of claudins varies considerably; most cell types express more than two claudins in various combinations to constitute mosaic TJ strands.Through the formation of TJ strands, claudins are directly involved in creating a primary barrier to the paracellular diffusion of solutes and water across epithelia (8). However, TJs are not a simple barrier: the barrier varies in tightness, measured by the transepithelial electrical resistance (R T ), and charge selectivity. Furuse et al. (9) reported that, when canine claudin-2 cDNA was transfected into high-resistance Madin-Darby canine kidney (MDCK) I cells primarily expressing claudins-1 and -4, the R T decreas...

The Ca2+-permeable cation channel TRPV4, which is part of the Trp family located in the circumventricular organs, is activated by cell swelling. To investigate the role of TRPV4 in osmotic sensation, we disrupted the TRPV4 gene in mice and examined the effect on osmotic metabolism. Disruption of the mouse TRPV4 gene did not influence either water intake behavior or serum osmolality. Short-term salt ingestion, however, seemed to impair the transient free water clearance. The level of serum arginine vasopressin (AVP) of TRPV4-/- mice was not significantly changed under normal conditions but was significantly increased under stimulated conditions. Incubation of brain slices with graded hyperosmolality suggested an exaggerated response of AVP secretion in TRPV4-/- mice. Thus TRPV4 in the brain may transmit a negative signal to AVP secretion similar to an inhibitory pass through the baroregulatory system. Thus, in the regulation of serum osmolality, TRPV4 is a swell-activated channel that appears to play a role in reversion toward hyposmolality.

By cable analysis and intracellular microelectrode impalement in the in vitro perfused renal tubule, we identified a-and f,-intercalated (IC) cells along the rabbit distal nephron segments, including the connecting tubule (CNT), the cortical collecting duct (CCD), and the outer medullary collecting duct in the inner stripe (OMCDj)

Endothelin (ET) is a potent and long-acting vasoconstrictor peptide consisting of 21 amino acids and recently isolated from a medium of cultured porcine endothelial cells. To determine the possible sites of ET action, we have conducted autoradiography and receptor binding assays with 125I-labeled ET in rat tissues. The displaceable binding sites of the ligand were widely distributed, not only in the arteries and heart but also in various other organs, e.g., brain, kidney, lung, adrenal gland, and intestine. The systemically injected ET did not cross the blood-brain barrier, whereas the ligand, applied in vitro, was mainly located in the hypothalamic and thalamic areas, lateral ventricular region, subfornical organ, globus pallidus, and caudate putamen. Both membrane preparations from the brain stem including diencephalon and from the heart ventricle had similar, specific, and high-affinity binding sites for 125I-ET. We suggest that ET is involved in the regulation of a large variety of organ functions and may also act as a neuropeptide.