Adaptation to odorants begins at the level of sensory receptor cells, presumably through modulation of their transduction machinery. The olfactory signal transduction involves the activation of the adenylyl cyclase/cyclic AMP second messenger system which leads to the sequential opening of cAMP-gated channels and Ca2+-activated chloride ion channels. Several reports of results obtained from in vitro preparations describe the possible molecular mechanisms involved in odorant adaptation; namely, ordorant receptor phosphorylation, activation of phosphodiesterase, and ion channel regulation. However, it is still unknown whether these putative mechanisms work in the intact olfactory receptor cell. Here we investigate the nature of the adaptational mechanism in intact olfactory cells by using a combination of odorant stimulation and caged cAMP photolysis which produces current responses that bypass the early stages of signal transduction (involving the receptor, G protein and adenylyl cyclase). Odorant- and cAMP-induced responses showed the same adaptation in a Ca2+-dependent manner, indicating that adaptation occurs entirely downstream of the cyclase. Moreover, we show that phosphodiesterase activity remains constant during adaptation and that an affinity change of the cAMP-gated channel for ligands accounts well for our results. We conclude that the principal mechanism underlying odorant adaptation is actually a modulation of the cAMP-gated channel by Ca2+ feedback.

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[Keywords: Myb; HIPK2; NLK; TAK1; phosphorylation; degradation] Supplemental material is available at http://www.genesdev.org.

Adipocyte differentiation is an important component of obesity, but how hormonal cues mediate adipocyte differentiation remains elusive. BMP stimulates in vitro adipocyte differentiation, but the role of BMP in adipogenesis in vivo is unknown. Drosophila Schnurri (Shn) is required for the signaling of Decapentaplegic, a Drosophila BMP homolog, via interaction with the Mad/Medea transcription factors. Vertebrates have three Shn orthologs, Shn-1, -2, and -3. Here, we report that Shn-2(-/-) mice have reduced white adipose tissue and that Shn-2(-/-) mouse embryonic fibroblasts cannot efficiently differentiate into adipocytes in vitro. Shn-2 enters the nucleus upon BMP-2 stimulation and, in cooperation with Smad1/4 and C/EBPalpha, induces the expression of PPARgamma2, a key transcription factor for adipocyte differentiation. Shn-2 directly interacts with both Smad1/4 and C/EBPalpha on the PPARgamma2 promoter. These results indicate that Shn-2-mediated BMP signaling has a critical role in adipogenesis.

SUMMARY1. Ionic selectivity of the conductance activated by n-amyl acetate (odorantactivated conductance) was analysed in isolated olfactory receptor cells under the whole-cell voltage clamp condition.2. Solitary receptor cells had a resting membrane potential of -44-7 + 70 mV (mean+ S.D.; n = 70). Application of 10 mM-n-amyl acetate caused a depolarizing response in about 30% of the cells. Sensitivity to the odorant was maximum at around the apical dendrite.3. Odorant induced an inward current to cells voltage clamped at their resting potential and bathed in the standard medium. The response amplitude was voltage dependent, and the polarity reversed at + 2-5 + 2-2 mV (n = 6). The I-V relation was almost linear at membrane potentials more positive than -20 mV, with an average slope of 3-14+ 1'59 nS (measured at 0 mV), but showed a marked outward rectification at voltages more negative than -30 mV.4. Removal of external Ca2+ increased the amplitude of the odorant-induced current and prolonged response duration, but did not cause a significant change on the reversal potential. Thus, Ca2+ affected the kinetics of the conductance, but did not seem to be a dominant charge carrier in the physiological condition. 6. The odorant-activated conducting channels were permeable to all alkali metal ions. The permeability ratios were; PLi :PNa :PK :PRb :PCS = 1-25:1:0 98 :084 :080.7. The present study strongly suggests that the olfactory receptor potential is generated by an increase in the membrane conductance to alkali metal ions.

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Abstract:Since skin is the first barrier separating the body from the external environment, impaired wound healing can be life threatening to living organisms. Delayed healing processes are observed in animals under certain circumstances, such as advanced age, diabetes, and immunosuppression, but the underlying mechanisms of the abnormality remain elusive. Redox homeostasis is defined as the balance between the levels of reactive oxygen species (ROS) and antioxidants in which antioxidative enzymes play central roles in scavenging ROS. In addition to deleterious effects, ROS also exert beneficial functions on some cellular processes such as transducing phosphorylation signaling, but excessive antioxidants may impede the healing process. Hence, strict control over the amounts of antioxidants is desirable when applied for therapeutic purposes. Here we overview recent findings regarding the relationships between antioxidative enzymes and wound healing. Unveiling the role of antioxidative enzymes is expected to contribute to our understanding of the wound healing processes.

Effects of L-glutamate (Glu), the neurotransmitter released by photoreceptors, on isolated cat bipolar cells were examined. Membrane currents of bipolar cells were recorded by the patch-clamp technique in a conventional whole-cell recording configuration using pipettes containing 1 mM cGMP, which has been known to activate a cationic current sensitive to Glu in ON-type bipolar cells. ON-type bipolar cells (depolarized by light in in situ) and OFF-type bipolar cells (hyperpolarized by light) were identified by their response polarity to Glu. When the whole-cell configuration was established, ON-type bipolar cells showed a steady inward current which was suppressed by Glu, consistent with the response polarity observed in in situ recordings. In contrast, OFF-type cells did not show a steady current during the recordings. However, they responded to Glu with an increase in cationic conductance. Among recorded cells, rod-driven bipolar cells were identified by their immunoreactivity to anti-protein kinase C (PKC-IR) antibody. Examination of PKC-IR revealed that ON-type bipolar cells included both rod- and cone-driven bipolar cells, while OFF-type cells were all cone-driven bipolar cells. The cGMP-activated current observed in ON-type cells was accompanied by a change in the current fluctuation due to the opening and closing of underlying channels. Fluctuation analysis gave a unitary conductance value of 13 pS. In half of the cells examined, maximum open probability reached almost 100%. The cGMP- activated channel in bipolar cells seems novel, fundamentally different from those found in photoreceptor cells or olfactory receptor cells.