Spatiotemporal temperature control by holographic heating microscopy unveils cellular thermosensitive calcium signalling

Optical microheating technologies have revealed how biological systems sense heating and cooling at the microscopic scale. Sensing is based on thermosensitive biochemical reactions that frequently engage membrane proteins, Ca²⁺ channels, and pumps to convert sensing information as the Ca²⁺ signalling in cells. These findings highlight the feasibility of thermally manipulating intracellular Ca²⁺ signalling. However, how the thermosensitive Ca²⁺ signalling would behave, particularly in multicellular systems, remains elusive. In this study, to extend the ability of the spatiotemporal temperature control by optical microheating technologies, we propose holographic heating microscopy. Water-absorbable infrared (IR) laser light is modulated by a reflective liquid crystal on a silicon spatial light modulator (LCOS-SLM). A computer-generated hologram displayed on the LCOS-SLM modulates the spatial phase pattern of the IR laser light to generate predesigned temperature gradients at the microscope focal plane. The holographic heating microscopy visualises how thermosensitive Ca²⁺ signalling is generated and propagated in MDCK cells, rat hippocampal neurons, and rat neonatal cardiomyocytes. Moreover, the optical control of the temporal temperature gradient reveals the cooling-rate dependency of Ca²⁺ signalling in HeLa cells. These findings demonstrate the extended ability of holographic heating microscopy in investigating cellular thermosensitivities and thermally manipulating cellular functions.