Fig. 1. Bone cells express Avprs. Immunofluorescence micrographs (A) and Western immunoblotting (B)show the expression of Avpr1α in osteoblasts and osteoclasts, and as a function of osteoblast (mineralization) and osteoclast (with Rankl) differentiation. The expression of Avp (ligand) and Avpr1α (receptor) in osteoblasts is regulated by 17β-estradiol, as determined by quantitative PCR (C) and Western immunoblotting (D). (Magnification: A, 63×.) Because Avp is a small peptide, its precursor neurophysin II is measured. Statistics: Student t test, P values shown compared with 0 h. Stimulation of Erk phosphorylation (p-Erk) as a function of total Erk (t-Erk) by Avp (10 −8 M) in osteoclast precursors (preosteoclasts), osteoclasts (OC), and osteoblasts establishes functionality of the Avpr1α in the presence or absence of the receptor inhibitor SR49059 (10 −8 M) (E). Western immunoblotting showing the expression of Avpr2 in preosteoclasts, OCs (F), and osteoblasts (G) isolated from Avpr1α −/− mice, as well as in MC3T3.E1 osteoblast precursors (G). Functionality of Avpr2 was confirmed by the demonstration that cells from Avpr1α −/− mice remained responsive to AVP in reducing the expression of osteoblast differentiation genes, namely Runx2, Osx, Bsp, Atf4, Opn, and Osteocalcin (quantitative PCR, P values shown) (H). Only relevant bands from Western blots are shown, with gaps introduced where empty lanes are excised to conserve space.

The sodium-activated potassium channel Slack (KNa1.1, Slo2.2, or Kcnt1) is highly expressed in populations of sensory neurons, where it mediates the sodium-activated potassium current (IKNa) and modulates neuronal activity. Previous studies suggest that Slack is involved in the processing of neuropathic pain. However, mechanisms underlying the regulation of Slack activity in this context are poorly understood. Using whole-cell patch-clamp recordings we found that Slack-mediated IKNa in sensory neurons of mice is reduced after peripheral nerve injury, thereby contributing to neuropathic pain hypersensitivity. Interestingly, Slack is closely associated with ATP-sensitive P2X3 receptors in a population of sensory neurons. In vitro experiments revealed that Slack-mediated IKNa may be bidirectionally modulated in response to P2X3 activation. Moreover, mice lacking Slack show altered nocifensive responses to P2X3 stimulation. Our study identifies P2X3/Slack signaling as a mechanism contributing to hypersensitivity after peripheral nerve injury and proposes a potential novel strategy for treatment of neuropathic pain.

The sustained component of the K(+) outward current in human atrial myocytes is believed to be due to the slowly inactivating ultra-rapid potassium current I Kur and not to the fast inactivating transient outward current Ito. Here we provide evidence for contribution of Ito to this late current due to the effects of dipeptidyl peptidase-like protein (DPP) 10 (DPP10a) interacting with Kv4.3 channels. We studied the late current component of Ito in human atrial myocytes and CHO cells co-expressing Kv4.3 or Kv4.3/KChIP2 (control) and DPP proteins using voltage-clamp technique and a pharmacological approach. A voltage dependent and slowly inactivating late current (43% of peak amplitude) could be observed in atrial myocytes. We found a similar current in CHO cells expressing Kv4.3/KChIP2 + DPP10a, but not in cells co-expressing Kv4.3 + DPP or Kv4.3/KChIP2 + DPP6-S. Assuming that DPP10a influences atrial Ito, we detected DPP10 expression of three alternatively spliced mRNAs, DPP10 protein and colocalization of Kv4.3 and DPP10 proteins in human atrial myocytes. DPP10a did not affect properties of expressed Kv1.5 excluding a contribution to the sustained IKur in atrial cells. To test for the contribution of Kv4-based Ito on sustained K(+) outward currents in human atrial myocytes, we used 4-AP to block IKur, in combination with Heteropoda toxin 2 to block Kv4 channels. We could clearly separate an Ito fraction of about 19% contributing to the late current in atrial myocytes. Thus, the interaction of DPP10a, expressed in human atrium, with Kv4.3 channels generates a sustained current component of Ito, which may affect late repolarization phase of atrial action potentials.

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