Potassium conductances and permeabilities are present in all nephron segments and serve various functions, such as K⁺ excretion and the maintenance of cell potential and volume. TASK-2 potassium channel has two pore-forming domains in tandem in each monomer and is sensitive to extracellular pH. Messenger RNA encoding TASK-2 can be detected in RNA derived from whole kidney (Reyes et al. 1998). As a first step to understanding the role of TASK-2 in the kidney, we have attempted to localise TASK-2 mRNA by RT-PCR of individual nephron segments.

Adult male mice were anaesthetised with sodium pentobarbitone, 100 mg kg^-1 I.P., and killed by decapitation. The kidneys were removed and divided into cortical and papillary sections by crude dissection, divided into 1 mm segments and digested with collagenase (0.5 mg ml^-1) at 37 °C in a shaking water bath for 30-60 min. Individual tubules were selected from the resulting tubule suspensions. Glomeruli and proximal tubules (PT) were identified by eye. Thick ascending limb (TAL) and cortical collecting tubule (CCT) segments were identified by the presence of mRNA for Tamm-Horsfall protein (THP) and aquaporin-2 (AQP-2), respectively. Amplification of endogenous β-actin mRNA was used as a positive control. Tubules were permeabilised with 0.5 % Triton X-100 and heating to 95 °C and reverse transcribed according to the manufacturer’s instructions (Promega). Reverse-transcribed material was subjected to two rounds of PCR: the first with multiplex primers specific to TASK-2, AQP-2, THP and β-actin, and the second with nested primers. PCR products were analysed by gel electrophoresis, stained with ethidium bromide and visualised by UV illumination. Reverse transcriptions were also performed in the absence of enzyme to control for contaminating genomic DNA.

TASK-2 mRNA was identified in all nephron segments tested including those positive for THP and AQP-2 mRNA which correspond to TAL and CCTs, respectively. PCR products were not a result of contamination or amplification of genomic DNA.

In conclusion, TASK-2 is expressed along the length of the mouse nephron. This expression pattern contrasts with that of TASK-1 (Morton et al. 1999), which was localised to glomeruli and proximal tubules only. Given its location throughout the nephron it may be involved in the regulation of electrogenic solute uptake by the proximal tubule and/or K⁺ excretion.

This work was supported by the Medical Research Council and The Wellcome Trust.

All procedures accord with current UK legislation.