Characterization and function of TWIK-related acid sensing K+ channels in a rat nociceptive cell

We examined the properties of a proton sensitive current in acutely dissociated, capsaicin insensitive nociceptive neurons from rat dorsal root ganglion (DRG). The current had features consistent with K+ leak currents of the KCNK family (TASK-1, TASK-3; TWIK-related acid sensing K+). Acidity and alkalinity induced inward and outward shifts in the holding current accompanied by increased and decreased whole cell resistance consistent with a K+ current. We used alkaline solutions to open the channel and examine its properties. Alkaline evoked currents (AECs; pH 10.0–10.75), reversed near the K+ equilibrium potential (−74 mV), and were suppressed 85% in 0mM K+. AECs were insensitive to Cs+ (1mM) and anandamide (1 μM), but blocked by Ba++ (1mM), quinidine (100 μM) or Ruthenium Red (10 μM). This pharmacology was identical to that of rat TASK-3 and inconsistent with that of TASK-1 or TASK-2. The TASK-like AEC was not modulated by PKA (forskolin, κ opioid agonists U69593 and GR8696, somatostatin) but was inhibited by PKC activator phorbol-12-myristate-13 acetate (PMA). When acidic solutions were used, we were able to isolate a Ba++ and Ruthenium Red insensitive current that was inhibited by Zn++. This Zn++ sensitive component of the proton sensitive current was consistent with TASK-1. In current clamp studies, acidic pH produced sensitive changes in resting membrane potential but did not influence excitability (pH 7.2–6.8). In contrast, Zn++ produced substantial changes in excitability at physiological pH. Alkaline solutions produced hyperpolarization followed by proportional burst discharges (pH 10.75–11.5) and increased excitability (at pH 7.4). In conclusion, multiple TASK currents were present in a DRG nociceptor and differentially contributed to distinct discharge mechanisms. [Copyright &y& Elsevier]