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 0 mM K(+). AECs were insensitive to Cs(+) (1 mM) and anandamide (1 microM), but blocked by Ba(++) (1 mM), quinidine (100 microM) or Ruthenium Red (10 microM). 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, kappa 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.
Cooper
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Department of Oral Surgery and Diagnostic Sciences, Division of Neuroscience, Box 100416, JHMHC, University of Florida College of Dentistry and McKnight Brain Institute, Gainesville, FL 32610, USA. bcooper@dental.ufl.edu
Johnson
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D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D024683:Potassium Channels, Tandem Pore Domain / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015032:Zinc / Q000378:metabolism
D004791:Enzyme Inhibitors; C487530:Kcnk1 protein, rat; D024683:Potassium Channels, Tandem Pore Domain; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D015032:Zinc