DEG/ENaC ion channels involved in sensory transduction are modulated by cold temperature

Abstract

Several DEG/ENaC cation channel subunits are expressed in the tongue and in cutaneous sensory neurons, where they are postulated to function as receptors for salt and sour taste and for touch. Because these tissues are exposed to large temperature variations, we examined how temperature affects DEG/ENaC channel function. We found that cold temperature markedly increased the constitutively active Na(+) currents generated by epithelial Na(+) channels (ENaC). Half-maximal stimulation occurred at 25 degrees C. Cold temperature did not induce current from other DEG/ENaC family members (BNC1, ASIC, and DRASIC). However, when these channels were activated by acid, cold temperature potentiated the currents by slowing the rate of desensitization. Potentiation was abolished by a "Deg" mutation that alters channel gating. Temperature changes in the physiologic range had prominent effects on current in cells heterologously expressing acid-gated DEG/ENaC channels, as well as in dorsal root ganglion sensory neurons. The finding that cold temperature modulates DEG/ENaC channel function may provide a molecular explanation for the widely recognized ability of temperature to modify taste sensation and mechanosensation.

Figure 1

Cold-induced stimulation of BNC1 proton-gated current. (A) Representative recordings of human BNC1 proton-activated (pH 4) current in Xenopus oocytes at the indicated temperatures (−60 mV). (B) Plot of proton-activated current (relative to maximal current, mean ± SEM, n = 7 or 8) for BNC1. Current level was determined by integrating the current from 0 to 35 s after pH addition. (C) Representative recordings of BNC1 proton-activated (pH 5) currents in COS-7 cells measured by whole-cell patch clamp (−70 mV). Traces are representative of four cells.

Figure 2

Modulation of ASIC and DRASIC by temperature. (A) Representative recordings of human ASIC and DRASIC proton-activated current (pH 5 and 4, respectively) in Xenopus oocytes at the indicated temperatures (−60 mV). (B) Arrhenius plot of the temperature dependence of the τ of DRASIC desensitization after activation by pH 4 (mean ± SEM, n = 6) and FaNaCh desensitization after activation by addition of 10 μM FMRFamide (mean ± SEM, n = 9 or 10). τ of desensitization was determined by single-exponential fits of the desensitization phase of the transient current.

Figure 3

Cold-induced stimulation of ENaC. Expression of α-, β-, and γhENaC in Xenopus oocytes. Whole-cell Na⁺ current was measured by two-electrode voltage clamp (−60 mV). (A) Representative current recording for wild-type ENaC at the indicated temperatures. Amiloride was added to bathing solution, as indicated, at a final concentration of 10 μM. (B) Plot of amiloride-sensitive Na⁺ current at the indicated membrane potentials for cells at 35°C or 10°C (mean ± SEM, n = 4). (C) Plot of amiloride-sensitive Na⁺ current (relative to maximal current) at temperatures from 6°C to 44°C (mean ± SEM, n = 8) for ENaC.

Figure 4

DEG mutations abolish cold-induced stimulation. Plot of amiloride-sensitive Na⁺ current (relative to maximal current) at temperatures from 6°C to 44°C in Xenopus oocytes expressing either β_S520K with α- and γhENaC, or BNC1_G430V (mean ± SEM, n = 8). Currents for wild-type ENaC and BNC1 (from Figs. 1 and 3) are included for comparison.

Figure 5

Temperature modulation of proton-gated current in sensory neurons. Whole-cell patch-clamp recording (−100 mV) of proton-activated current (pH 6) in cultured DRG neurons at the indicated temperatures. The traces are representative of six cells.