Exciting cell membranes with a blustering heat shock

Area of Science:

• Biophysics
• Cellular Neuroscience
• Molecular Biology

Background:

• Pulsed laser light can induce brief heat shocks in cells.
• These heat shocks can evoke action potentials in neurons and contractions in cardiomyocytes.
• The underlying biophysical mechanism remains largely unknown.

Purpose of the Study:

• To elucidate the biophysical mechanism of photothermal heat shock-induced currents.
• To investigate the role of temperature change rate versus absolute temperature.
• To model the resulting cellular membrane potential changes.

Main Methods:

• Utilized Caenorhabditis elegans neuromuscular junctions.
• Applied rapid heat shocks (500°C/s for 500 μs) using pulsed laser light.
• Measured evoked excitatory currents, charge injection, and temperature changes.
• Analyzed voltage-dependence and thermal relaxation dynamics.
• Developed a quantitative model for membrane potential modulation.

Main Results:

• A 500°C/s heat shock evoked ~35 pA excitatory current and injected ~23 fC charge.
• Cellular temperature increased by only 0.25°C.
• The rate of temperature change (dT/dt) was the critical factor, not the peak temperature.
• The current was voltage-dependent, attributed to thermally driven ion displacement near the plasma membrane.
• Asymmetrical capacitive currents caused brief cellular depolarization.

Conclusions:

• Photothermal heat shock currents are driven by the rate of temperature change.
• This mechanism involves voltage-dependent, thermally driven ion displacement.
• The findings provide a quantitative model for optical heat shock applications in cellular studies.