Green’s function representation of laser induced thermal dynamics and determination of thermal criteria for optically induced neural activation

Exciting Cell Membranes with a Blustering Heat Shock

“…1 a shows the temperature rise generated in media by a single IR optical pulse (average, n ¼ 38) determined by measuring the impedance change of a calibrated glass pipette (inset, example impedance change for one pulse). The temperature increased linearly in time during the IR pulse because the laser pulse was much shorter than the thermal relaxation time (linearity confirmed for IR pulses up to 3 ms, R 2 > 0.99; n ¼ 5) (11). We define the heat shock stimulus as the time rate of change of temperature dT/dt, which was a constant~500 C/s during the stimulus shown and became slightly negative during relaxation ( Fig.…”

“…Transient heat pulses, delivered to cells by absorption of infrared (IR) light by water, have been shown to modulate intracellular signaling (1,2), trigger action potential generation and neurotransmitter release in neurons (3)(4)(5)(6)(7), and evoke contraction in cardiomyocytes (2,8,9). Cells are sensitive to the magnitude of temperature change (DT) delivered by each pulse as well as the time rate of change of temperature during the pulse, or heat shock (dT/dt) (10,11). Sensitivity reported in the literature, however, is highly variable due to diversity in the endogenous expression of temperature-sensitive ion channels and molecular signaling cascades, and differences in optical stimulus parameters used between different studies (12)(13)(14)(15)(16).…”