Figure 4: Hyperosmotic stimuli evoke membrane currents in heterologously expressing mouse TRPM8 CHO cells and Trpm8+/EGFPf DRG neurons.
From: TRPM8 is a neuronal osmosensor that regulates eye blinking in mice
The osmolality was altered by addition of sucrose to keep the ionic gradients constant in a–f. (a) Representative current responses evoked by depolarizing voltage ramps in CHO cells expressing TRPM8 channels. Voltage ramps (2 s duration) from −60 to +100 mV in 317 mOsm kg−1 and hyperosmotic (667 mOsm kg−1) extracellular solutions. (b) Osmotically activated outward (top trace, +60 mV) and inward (bottom trace, −60 mV) currents in a TRPM8-expressing CHO cell. Horizontal bars indicate application of hyperosmotic solutions. (c) Voltage (current clamp) recording demonstrating membrane depolarization and action potential firing evoked by hyperosmotic solutions in EGFP-positive neurons from a Trpm8+/EGFPf mouse and the effect of the TRPM8 antagonist AMTB (20 μM). Note that application of AMTB evoked hyperpolarizations in TRPM8-expressing neurons (inset box, scale bars indicate 10 mV and 10 s). (d) Outward (top trace, +60 mV) and inward (bottom trace. −60 mV) currents evoked by a hyperosmotic solution (467 mOsm kg−1) in EGFP-positive DRG neurons from a Trpm8+/EGFPf mouse. Inward current was associated with action currents from neurites in some neurons. (e) Outward current evoked by a hyperosmotic solution at +60 mV in a neuron from Trpm8+/EGFPf mouse and the effect of AMTB. Note reduction in holding current in the presence of AMTB consistent with inhibition of voltage activated TRPM8 channels. Dotted line indicates the zero current level. (f) Effect of hyperosmotic solutions on membrane potential of EGFP-positive neurons from Trpm8+/EGFPf mice (left) and Trpm8EGFPf /EGFPf (knockout) mice (right).
