However, the area of pERK positive fibers per blood vessel was comparable between Trpv4−/− mice and controls (compare Figure 7B with Figure 7C). It may be that basal activation of pERK in sensory fibers is already altered in the absence of TRPV4 channels. Together these results indicate that the presence of TRPV4 is necessary for hypo-osmotic stimuli to activate hepatic osmoreceptors. To gauge the potential influence of Compound Library hepatic afferents in regulating blood osmolality in humans, we conducted an investigation of a large cohort of liver transplant recipients. We found that the blood osmolality of the liver transplant

group (n = 40, age range 21–74 years) was slightly (∼2 mOsm), but significantly (p < 0.05 Student`s t test) elevated compared to a control age Adriamycin manufacturer matched cohort (n = 57, age range 23–61 years) (Figure 7E). The levels of the C-terminal pro-arginine-vasopressin (copeptin) were also significantly elevated in samples from liver transplantees (15 ± 4.8 pmol/l) compared to healthy controls (4.16 ± 0.4 pmol/l; p < 0.01, Student's t test). Copeptin is a stable marker of vasopressin levels, which is upregulated in patients with experimentally induced

increases in blood osmolality (Szinnai et al., 2007), the upregulation seen here suggests normal central osmoregulation in liver transplantees. These findings, which will be followed up in a more detailed longitudinal clinical study, suggest that hepatic afferents may also contribute to human osmoregulation. Here, we have identified a specific population of TRPV4-positive hepatic sensory afferents that detect physiological changes in blood osmolality. We show that the in vivo activation of hepatic afferents by physiological changes in hepatic portal vein osmolality is absent Thymidine kinase in Trpv4−/− mutant mice. Strikingly, hepatic thoracic sensory neurons possess a fast and sensitive osmosensitive current that can dynamically signal

physiologically relevant hypo-osmotic shifts in blood osmolality. We have also shown that identified small hepatic sensory neurons completely lack the osmosensitive current in Trpv4−/− mice. The pharmacological and biophysical characteristics of the osmosensitive current in hepatic afferents together with the genetic evidence, suggests that this current is, at least in part, mediated by TRPV4 channels ( Figure 2 and Figure 6). In summary, we have characterized, in detail, the cellular and molecular properties of a novel population of hepatic afferents that in humans probably forms the afferent arm of an important regulatory reflex involved in the regulation of metabolism, blood pressure, and osmolality homeostasis. Peripheral sensory neurons that function as osmosensors have received little attention, although there is literature indicating their existence in animals (Adachi, 1984, Adachi et al.