Cell swelling increases intracellular calcium in Necturus erythrocytes.
This study examined the role of Ca(2+) in regulatory volume decrease by Necturus erythrocytes. Hypotonic shock (50% tonicity) stimulated an increase in cytosolic free Ca(2+), detected using epi-fluorescence microscopy and the fluorescent Ca(2+) indicator fluo-4-AM (10 microM). A similar increase in fluorescence did not occur under isosmotic conditions, unless cells were exposed to the Ca(2+) ionophore A23187 (0.5 microM). In addition, a low Ca(2+) medium (amphibian Ringer solution with 5 mM EGTA), hexokinase (2.5 U/ml, an ATP scavenger), suramin (100 microM, a P2 receptor antagonist) and gadolinium (10 microM, a stretch-activated channel blocker) each inhibited the swelling-induced increase in Ca(2+). Consistent with these studies, a low Ca(2+) Ringer solution increased osmotic fragility, whereas volume recovery following hypotonic shock (measured with a Coulter counter) was potentiated with A23187 (0.5 microM). By contrast, a low Ca(2+) extracellular medium or buffering intracellular Ca(2+) with BAPTA-AM (100 microM) reduced the rate of volume recovery following hypotonic challenge. Finally, a low Ca(2+) extracellular Ringer solution inhibited whole-cell currents that are activated during cell swelling (measured with the whole-cell patch clamp technique). Our results are most consistent with hypotonic shock causing an increase in cytosolic free Ca(2+), thereby stimulating subsequent volume decrease.
Light
Douglas B
DB
Department of Biology, Ripon College, Ripon, WI 54971, USA. lightd@ripon.edu
Attwood
Andrew J
AJ
Siegel
Corryn
C
Baumann
Nicole L
NL
D000818:Animals; D002118:Calcium / Q000172:deficiency*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D048429:Cell Size / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D007038:Hypotonic Solutions / Q000494:pharmacology; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism*; D007476:Ionophores / Q000494:pharmacology; D009338:Necturus maculosus; D009997:Osmotic Pressure / Q000187:drug effects; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D005456:Fluorescent Dyes; D007038:Hypotonic Solutions; D007476:Ionophores; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D002118:Calcium