Abstract
Lysosomes are acidic Ca2+ stores often mobilised in conjunction with endoplasmic reticulum (ER) Ca2+ stores. GPN is a widely used lysosomotropic agent that evokes cytosolic Ca2+ signals in many cells. But whether these signals are due to a primary action on lysosomes is unclear in light of recent evidence showing GPN mediates direct ER Ca2+ release through changes in cytosolic pH. Here, we show that GPN evoked rapid increases in cytosolic pH but slower Ca2+ signals. NH4Cl evoked comparable changes in pH but failed to affect Ca2+. The V-type ATPase inhibitor, bafilomycin A1, increased lysosomal pH over a period of hours. Acute treatment modestly affected lysosomal pH and potentiated Ca2+ signals evoked by GPN. In contrast, chronic treatment led to more profound changes in luminal pH and selectively inhibited GPN-action. GPN blocked Ca2+ responses evoked by the novel NAADP-like agonist, TPC2-A1-N. GPN-evoked Ca2+ signals were thus better correlated with associated pH changes in the lysosome compared to the cytosol and coupled to lysosomal Ca2+ release. We conclude that Ca2+ signals evoked by GPN most likely derive from acidic organelles.
- Received November 3, 2020.
- Accepted January 21, 2021.
- © 2021. Published by The Company of Biologists Ltd
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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