We have cloned a novel member of the tandem pore K+ channel family from human brain cDNA. The novel cDNA encodes a 330-residue polypeptide of predicted molecular mass 36 kDa. We have named the channel TASK-5 owing to its sequence homology with TASK-1 and TASK-3. TASK-5 mRNA is expressed in pancreas, liver, kidney, lung, ovary, testis and heart. However, expression of TASK-5 in heterologous systems failed to elicit ionic currents. Removal of a putative endoplasmic reticulum retention sequence did not alter this finding and the distribution of channel proteins in HEK293 cells was similar for both TASK-1 and TASK-5. We tested whether TASK-5 could form heteromers with TASK-1. We show a mutant form of TASK-1 (H98N) to have a radically reduced sensitivity to acidification. Proton sensitivity could be rescued by injecting equimolar amounts of wild-type and mutant TASK-1 cRNA into Xenopus oocytes; the effect was that expected if half the channels formed are heteromers. Co-expression of TASK-5 with TASK-1 H98N does not affect the proton sensitivity of mutant TASK-1; thus TASK-5 appears not to form heteromers with TASK-1. Nonetheless, TASK-5 may require some other, unidentified partner subunit to form functional channels in the plasma membrane or it may form a channel in an intracellular organelle.

Field measurements of the vertical profiles of horizontal fluxes of airborne, sand‐sized soil aggregates are shown to be in good agreement with solutions of an equation that express the dependence of the concentration of sand at a given height on vertical diffusion and sedimentation. This approach treats sand as a diffusing agent rather than as projectiles that are affected by the wind only on the horizontal direction. The observed horizontal sand fluxes are shown to be in agreement with empirical formulas that express total horizontal flux of sand as a function of wind and soil parameters.

moved and the residual viscous red oil treated with 5 cc. of boiling petroleum ether (b. p. 60-110"). The insoluble dark gum was removed from the solution by decantation of the latter. On cooling, the petroleum ether deposited an orange-colored solid which weighed 235 mg. By concentrating the mother liquors, carefully discarding the red gum which formed regularly, another 540 mg. of this solid was obtained. The total yield was 775 mg. (26%). A sample was recrystallized from petroleum ether (Darco) to constant melting point; tiny needles, m. p. 146' (cor.). Anal. Calcd. for C~lH2604: C, 72.88; H, 7.89. Found: C, 73.55; H, 7.82.l-Hydroxy-J-n-amyl-9-rnethyl-6-dibenzopyrone.-A mixture of 235 mg. of 2,6-dimethoxy-4-n-amyl-5'-methyl-2'-carboxybiphenyl, 0.6 cc. of 48% hydrobromic acid, 1 cc. of glacial acetic acid, and 0.5 cc. of acetic anhydride was heated to reflux to dissolve the solid acid, and heating continued for four hours. After pouring into 20 cc. of water, the reaction mixture was extracted three times with ether and the organic layer washed thoroughly with saturated aqueous sodium bicarbonate and dried over magnesium sulfate. The solvent was removed and the oily residue was treated with boiling petroleum ether (b. p.

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summaryA channel was identified in cell-attached recordings in rat hippocampal neurones maintained in culture. This channel, which was highly active at the resting membrane potential, was present in most (73%) patches studied. The channel was characterized by long duration openings and a high open probability (Pï, mean value 0·73 at −70 mV) at negative patch potentials with mild voltage dependence over the range −40 to −120 mV. It showed inward rectification. There were up to five active channels in cell-attached recordings in experiments where the cells were bathed in sodiumcontaining Locke solution. The single channel conductances in cell-attached recordings with 140 or 40 mÒ K¤ in the patch pipette were 26 and 12 pS, respectively. The channel was therefore selective for K¤ over Na¤. The channel was not permeable to Rb¤ ions. The single channel conductance was 24 pS in excised inside-out patches bathed in symmetrical K¤ (140 mÒ) solutions. Examination of the channel kinetics revealed that both the open and closed time distributions could be fitted by the sum of three exponentials, there being no pronounced voltage sensitivity between −60 and −120 mV. The 26 pS K¤ channel was insensitive to extracellular TEA, apamin, 4-AP and dequalinium. Neither was it sensitive to intracellular Ca¥. Extracellular Ba¥ was effective in reversibly blocking the channel, the IC50 being 2·0 mÒ. There was no obvious effect of bath application of the K¤ channel opener, lemakalim, or a cAMP analogue. This channel appears to contribute a significant proportion (at least 30%) of the resting conductance in these neurones. introduction Hippocampal neurones in culture possess a number of K¤ channel subtypes the functions of which include setting the resting membrane potential, determining the electrical threshold, shaping the action potential, generating the after-hyperpolarization and controlling action potential discharge patterns (see Halliwell, 1990). Some of these channel types have been described in detail in either hippocampal or other central neurones in both macroscopic current measurements