From a systematic screening of animal venoms, we isolated a new toxin (APETx2) from the sea anemone Anthopleura elegantissima , which inhibits ASIC3 homomeric channels and ASIC3‐containing heteromeric channels both in heterologous expression systems and in primary cultures of rat sensory neurons. APETx2 is a 42 amino‐acid peptide crosslinked by three disulfide bridges, with a structural organization similar to that of other sea anemone toxins that inhibit voltage‐sensitive Na+ and K+ channels. APETx2 reversibly inhibits rat ASIC3 (IC50=63 nM), without any effect on ASIC1a, ASIC1b, and ASIC2a. APETx2 directly inhibits the ASIC3 channel by acting at its external side, and it does not modify the channel unitary conductance. APETx2 also inhibits heteromeric ASIC2b+3 current (IC50=117 nM), while it has less affinity for ASIC1b+3 (IC50=0.9 μM), ASIC1a+3 (IC50=2 μM), and no effect on the ASIC2a+3 current. The ASIC3‐like current in primary cultured sensory neurons is partly and reversibly inhibited by APETx2 with an IC50 of 216 nM, probably due to the mixed inhibitions of various co‐expressed ASIC3‐containing channels.

A complementary DNA encoding a novel K⁺ channel, called TASK-2, was isolated from human kidney and its gene was mapped to chromosome 6p21. TASK-2 has a low sequence similarity to other two pore domain K⁺ channels, such as TWIK-1, TREK-1, TASK-1, and TRAAK (18–22% of amino acid identity), but a similar topology consisting of four potential membrane-spanning domains. In transfected cells, TASK-2 produces noninactivating, outwardly rectifying K⁺ currents with activation potential thresholds that closely follow the K⁺equilibrium potential. As for the related TASK-1 and TRAAK channels, the outward rectification is lost at high external K⁺concentration. The conductance of TASK-2 was estimated to be 14.5 picosiemens in physiological conditions and 59.9 picosiemens in symmetrical conditions with 155 mm K⁺. TASK-2 currents are blocked by quinine (IC₅₀ = 22 μm) and quinidine (65% of inhibition at 100 μm) but not by the other classical K⁺ channel blockers tetraethylammonium, 4-aminopyridine, and Cs⁺. They are only slightly sensitive to Ba²⁺, with less than 17% of inhibition at 1 mm. As TASK-1, TASK-2 is highly sensitive to external pH in the physiological range. 10% of the maximum current was recorded at pH 6.5 and 90% at pH 8.8. Unlike all other cloned channels with two pore-forming domains, TASK-2 is essentially absent in the brain. In human and mouse, TASK-2 is mainly expressed in the kidney, where in situ hybridization shows that it is localized in cortical distal tubules and collecting ducts. This localization, as well as its functional properties, suggest that TASK-2 could play an important role in renal K⁺ transport.

Aldosterone and vasopressin are responsible for the final adjustment of sodium and water reabsorption in the kidney. In principal cells of the kidney cortical collecting duct (CCD), the integral response to aldosterone and the long-term functional effects of vasopressin depend on transcription. In this study, we analyzed the transcriptome of a highly differentiated mouse clonal CCD principal cell line (mpkCCD _cl4 ) and the changes in the transcriptome induced by aldosterone and vasopressin. Serial analysis of gene expression (SAGE) was performed on untreated cells and on cells treated with either aldosterone or vasopressin for 4 h. The transcriptomes in these three experimental conditions were determined by sequencing 169,721 transcript tags from the corresponding SAGE libraries. Limiting the analysis to tags that occurred twice or more in the data set, 14,654 different transcripts were identified, 3,642 of which do not match known mouse sequences. Statistical comparison (at P < 0.05 level) of the three SAGE libraries revealed 34 AITs (aldosterone-induced transcripts), 29 ARTs (aldosterone-repressed transcripts), 48 VITs (vasopressin-induced transcripts) and 11 VRTs (vasopressin-repressed transcripts). A selection of the differentially-expressed, hormone-specific transcripts (5 VITs, 2 AITs and 1 ART) has been validated in the mpkCCD _cl4 cell line either by Northern blot hybridization or reverse transcription–PCR . The hepatocyte nuclear transcription factor HNF-3-α (VIT39), the receptor activity modifying protein RAMP3 (VIT48), and the glucocorticoid-induced leucine zipper protein (GILZ) (AIT28) are candidate proteins playing a role in physiological responses of this cell line to vasopressin and aldosterone.

Two novel K⁺ channel α subunits, named Kv9.1 and Kv9.2, have been cloned. The Kv9.2 gene is situated in the 8q22 region of the chromosome. mRNAs for these two subunits are highly and selectively expressed in the nervous system. High levels of expressions are found in the olfactory bulb, cerebral cortex, hippocampal formation, habenula, basolateral amygdaloid nuclei, and cerebellum. Interestingly Kv9.1 and Kv9.2 colocalized with Kv2.1 and/or Kv2.2 α subunits in several regions of the brain. Neither Kv9.1 nor Kv9.2 have K⁺ channel activity by themselves, but both modulate the activity of Kv2.1 and Kv2.2 channels by changing kinetics and levels of expression and by shifting the half-inactivation potential to more polarized values. This report also analyzes the changes in electrophysiological properties of Kv2 subunits induced by Kv5.1 and Kv6.1, two other modulatory subunits. Each modulatory subunit has its own specific properties of regulation of the functional Kv2 subunits, and they can lead to extensive inhibitions, to large changes in kinetics, and/or to large shifts in the voltage dependencies of the inactivation process. The increasing number of modulatory subunits for Kv2.1 and Kv2.2 provides an amazingly new capacity of functional diversity.