biostudies-literatureYeh SAU.S. Department of Health & Human Services | NIH | National Institute of Dental and Craniofacial ResearchNIDCR NIH HHSNew Jersey Health FoundationNIDDK NIH HHSNHLBI NIH HHSU.S. Department of Health & Human Services | NIH | National Heart, Lung, and Blood InstituteNIAAA NIH HHSU.S. Department of Health & Human Services | NIH | National Institute of Diabetes and Digestive and Kidney DiseasesU.S. Department of Health & Human Services | NIH | National Institute on Alcohol Abuse and Alcoholism393https://www.ebi.ac.uk/biostudies/studies/S-EPMC8770570biostudies-literatureUnknown13(1)The fate of hematopoietic stem cells (HSCs) can be directed by microenvironmental factors including extracellular calcium ion concentration ([Ca2+]e), but the local [Ca2+]e around individual HSCs in vivo remains unknown. Here we develop intravital ratiometric analyses to quantify the absolute pH and [Ca2+]e in the mouse calvarial bone marrow, taking into account the pH sensitivity of the calcium probe and the wavelength-dependent optical loss through bone. Unexpectedly, the mean [Ca2+]e in the bone marrow (1.0 ± 0.54 mM) is not significantly different from the blood serum, but the HSCs are found in locations with elevated local [Ca2+]e (1.5 ± 0.57 mM). With aging, a significant increase in [Ca2+]e is found in M-type cavities that exclusively support clonal expansion of activated HSCs. This work thus establishes a tool to investigate [Ca2+]e and pH in the HSC niche with high spatial resolution and can be broadly applied to other tissue types.Nature communicationsQuantification of bone marrow interstitial pH and calcium concentration by intravital ratiometric imaging.PMC8770570P01 HL142494PC 57-20R01 DK115577R01 DK123216R21 AA028340R21AA028340R01 DE026155Wu JWHou JYu SZhang YBelfield KDLin CPYeh SACamargo FDfalseQuantification of bone marrow interstitial pH and calcium concentration by intravital ratiometric imaging.The fate of hematopoietic stem cells (HSCs) can be directed by microenvironmental factors including extracellular calcium ion concentration ([Ca2+]e), but the local [Ca2+]e around individual HSCs in vivo remains unknown. Here we develop intravital ratiometric analyses to quantify the absolute pH and [Ca2+]e in the mouse calvarial bone marrow, taking into account the pH sensitivity of the calcium probe and the wavelength-dependent optical loss through bone. Unexpectedly, the mean [Ca2+]e in the bone marrow (1.0 ± 0.54 mM) is not significantly different from the blood serum, but the HSCs are found in locations with elevated local [Ca2+]e (1.5 ± 0.57 mM). With aging, a significant increase in [Ca2+]e is found in M-type cavities that exclusively support clonal expansion of activated HSCs. This work thus establishes a tool to investigate [Ca2+]e and pH in the HSC niche with high spatial resolution and can be broadly applied to other tissue types.2022-01-01T00:00:00Z2022 Jan2026-06-04T04:31:30.525Z2025-04-06T01:21:21.867ZS-EPMC87705703504641110.1038/s41467-022-27973-x