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A subset of taste receptor cells express biocytin‐permeable channels activated by reducing extracellular Ca2+ concentration

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Taste receptor cells (type II cells) transmit taste information to taste nerve fibres via ATP‐permeable channels, including calcium homeostasis modulator (CALHM), connexin and/or pannexin1 channels, via the paracrine release of… Click to show full abstract

Taste receptor cells (type II cells) transmit taste information to taste nerve fibres via ATP‐permeable channels, including calcium homeostasis modulator (CALHM), connexin and/or pannexin1 channels, via the paracrine release of adenosine triphosphate (ATP) as a predominant transmitter. In the present study, we demonstrate that extracellular Ca2+‐dependent biocytin‐permeable channels are present in a subset of type II cells in mouse fungiform taste buds using biocytin uptake, immunohistochemistry and in situ whole‐cell recordings. Type II cells were labelled with biocytin in an extracellular Ca2+ concentration ([Ca2+]out)‐sensitive manner. We found that the ratio of biocytin‐labelled type II cells to type II cells per taste bud was approximately 20% in 2 mM Ca2+ saline, and this ratio increased to approximately 50% in nominally Ca2+‐free saline. The addition of 300 µM GdCl3, which inhibits various channels including CALHM1 channels, significantly inhibited biocytin labelling in nominally Ca2+‐free saline, whereas the addition of 20 µM ruthenium red did not. Moreover, Cs+‐insensitive currents increased in nominally Ca2+‐free saline in approximately 40% of type II cells. These increased currents appeared at a potential of above −35 mV, reversed at approximately +10 mV and increased with depolarization. These results suggest that biocytin labels type II cells via ion channels activated by [Ca2+]out reduction, probably “CALHM‐like” channels, on the basolateral membrane and that taste receptor cells can be categorized into two groups based on differences in the expression levels of [Ca2+]out‐dependent biocytin‐permeable channels. These data indicate electrophysiological and pharmacologically relevant properties of biocytin‐permeable channels and suggest their contributions to taste signal transduction.

Keywords: taste; permeable channels; biocytin permeable; biocytin; ca2; type cells

Journal Title: European Journal of Neuroscience
Year Published: 2020

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