Positive-going hybrid indicators for voltage imaging in excitable cells and tissues

Membrane potential dynamics are crucial to the physiology of electrically
excitable cells, such as neurons, cardiomyocytes, and pancreatic islet
cells. Fluorescent voltage indicators have enabled the visualization of
electrical activities at the single-cell level across large cell
populations. However, most existing indicators have a negative
fluorescence-voltage response, resulting in a high background signal when
cells are at their resting state. To reduce background interference during
voltage imaging, we developed a positive-going hybrid voltage indicator
(HVI+), which has a lower intensity at the resting state and becomes
brighter upon membrane depolarization. HVI+-Cy3b exhibits a remarkable
voltage sensitivity of 55% ΔF/F0 per 100 mV, enabling accurate reporting
of action potential waveforms in beating cardiomyocytes and neurons.
Additionally, by combining HVI+-Cy3b with HVI-Cy3b, we demonstrate the
capability to simultaneously assess the effects of glucose on the spike
activities of two cell types in pancreatic islets.

膜电位动态变化对神经元、心肌细胞、胰岛细胞等电兴奋性细胞的生理功能至关重要。荧光电压指示剂已实现对大细胞群体中单细胞水平电活动的可视化观测。然而，绝大多数现有指示剂均呈现负向荧光-电压响应，导致细胞处于静息状态时背景信号偏高。为降低电压成像过程中的背景干扰，本研究开发了正向混合型电压指示剂（positive-going hybrid voltage indicator, HVI+），该指示剂在细胞静息状态下荧光强度更低，而在细胞膜去极化时亮度会升高。HVI+-Cy3b展现出优异的电压敏感性：每100 mV电位变化对应55%的ΔF/F0变化，可精准记录搏动心肌细胞与神经元的动作电位波形。此外，通过将HVI+-Cy3b与HVI-Cy3b联用，本研究证实其可同时评估葡萄糖对胰岛内两种细胞锋电位活动的影响。