Cultured mesenchymal stromal cells (MSCs) from different sources represent a heterogeneous population of proliferating non-differentiated cells that contains multipotent stem cells capable of originating a variety of mesenchymal cell lineages. Despite tremendous progress in MSC biology spurred by their therapeutic potential, current knowledge on receptor and signaling systems of MSCs is mediocre. Here we isolated MSCs from the human adipose tissue and assayed their responsivity to GPCR agonists with Ca(2+) imaging. As a whole, a MSC population exhibited functional heterogeneity. Although a variety of first messengers was capable of stimulating Ca(2+) signaling in MSCs, only a relatively small group of cells was specifically responsive to the particular GPCR agonist, including noradrenaline. RT-PCR and immunocytochemistry revealed expression of α1B-, α2A-, and β2-adrenoreceptors in MSCs. Their sensitivity to subtype-specific adrenergic agonists/antagonists and certain inhibitors of Ca(2+) signaling indicated that largely the α2A-isoform coupled to PLC endowed MSCs with sensitivity to noradrenaline. The all-or-nothing dose-dependence was characteristic of responsivity of robust adrenergic MSCs. Noradrenaline never elicited small or intermediate responses but initiated large and quite similar Ca(2+) transients at all concentrations above the threshold. The inhibitory analysis and Ca(2+) uncaging implicated Ca(2+)-induced Ca(2+) release (CICR) in shaping Ca(2+) signals elicited by noradrenaline. Evidence favored IP3 receptors as predominantly responsible for CICR. Based on the overall findings, we inferred that adrenergic transduction in MSCs includes two fundamentally different stages: noradrenaline initially triggers a local and relatively small Ca(2+) signal, which next stimulates CICR, thereby being converted into a global Ca(2+) signal.

Specialized Ca(2+)-dependent ion channels ubiquitously couple intracellular Ca(2+) signals to a change in cell polarization. The existing physiological evidence suggests that Ca(2+)-activated Cl(-) channels (CaCCs) are functional in taste cells. Because Ano1 and Ano2 encode channel proteins that form CaCCs in a variety of cells, we analyzed their expression in mouse taste cells. Transcripts for Ano1 and Ano2 were detected in circumvallate (CV) papillae, and their expression in taste cells was confirmed using immunohistochemistry. When dialyzed with CsCl, taste cells of the type III exhibited no ion currents dependent on cytosolic Ca(2+). Large Ca(2+)-gated currents mediated by TRPM5 were elicited in type II cells by Ca(2+) uncaging. When TRPM5 was inhibited by triphenylphosphine oxide (TPPO), ionomycin stimulated a small but resolvable inward current that was eliminated by anion channel blockers, including T16Ainh-A01 (T16), a specific Ano1 antagonist. This suggests that CaCCs, including Ano1-like channels, are functional in type II cells. In type I cells, CaCCs were prominently active, blockable with the CaCC antagonist CaCCinh-A01 but insensitive to T16. By profiling Ano1 and Ano2 expressions in individual taste cells, we revealed Ano1 transcripts in type II cells only, while Ano2 transcripts were detected in both type I and type II cells. P2Y agonists stimulated Ca(2+)-gated Cl(-) currents in type I cells. Thus, CaCCs, possibly formed by Ano2, serve as effectors downstream of P2Y receptors in type I cells. While the role for TRPM5 in taste transduction is well established, the physiological significance of expression of CaCCs in type II cells remains to be elucidated.

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