Capsaicin-Induced Changes in the Cytosolic Calcium Level and Mitochondrial Membrane Potential

Simultaneous video-microfluorimetry allows experimenters to monitor calcium signals in the cytosol, as well as changes in the membrane potential of the mitochondria, in living cells loaded with both fura2 and rhodamine123 (rhod123). Capsaicin-evoked responses of cultured sensory neurons and transfected HT1080 cells are described below. Polymodal nociceptors [1] or other cells expressing TRPV1 receptors respond to capsaicin application with a rise in the cytosolic calcium level ([Ca2+](c)), reaching eventually toxic levels. Capsaicin induces selective permanent morphological changes of the mitochondria before any loss of small cells (type B) in the sensory ganglia can be detected [3]. An unknown link between changes in the mitochondria and cell loss can be investigated by combined functional examination of capsaicin-induced [Ca2+](c) changes and reactions of the mitochondria. In most tests, the capsaicin-induced [Ca2+](c) elevation occurred before the rising phase of rhod123 waves. Cellular reactions were either transient or sustained (lasting over hundreds of seconds). A transient or a sustained nature of the reactions was slightly concentration-dependent. Fluorescence of the cells changed in complicated ways during repeated tests. Moderate but permanent changes of the cellular responsiveness suggest mild injury, which might be involved in cellular desensitization.