Isolation and characterization of membrane potential changes associated with release of calcium from intracellular stores in rat thymic lymphocytes.
Membrane potential changes accompanying Ca2+ influx stimulated by release of Ca2+ from intracellular stores (store-regulated Ca2+ uptake) were monitored in BAPTA-loaded rat thymic lymphocytes using the fluorescent indicator bis(1,3-diethylthiobarbituric acid)trimethine oxonol. Depletion of [Ca2+]i stores by the application of thapsigargin, ionomycin or cyclopiazonic acid induced a depolarization which was (i) dependent upon BAPTA-loading, (ii) dependent upon extracellular Ca2+, (iii) independent of extracellular Na+ and (iv) abolished by 5 mM extracellular Ni2+. This depolarization was followed by a charybdotoxin-sensitive repolarization and subsequent hyperpolarization to values approximating the K+ equilibrium potential, consistent with secondary activation of a K+ conductance. These membrane potential changes temporally correlated with Ca2+ influx from the extracellular medium as measured fluorimetrically with indo-1. The divalent cation permeability sequence was investigated by monitoring the magnitude of the depolarization observed following the addition of 4 mM Ca2+, Mn2+, Ba2+ or Sr2+ to cells pretreated with doses of thapsigargin or ionomycin known to activate the store-regulated calcium uptake pathway. On the basis of these experiments, we conclude that the store-regulated Ca2+ uptake pathway has the following permeability sequence: Ca2+ > Mn2+ >> Ba2+, Sr2+ with Mn2+ displaying significant permeability relative to Ca2+. This pathway is distinguishable from other divalent cation uptake pathways reported in other cells types on the basis of its activation by thapsigargin and its high Mn2+ permeability.
Wilson
O I
OI
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Marriott
I
I
Mahaut-Smith
M P
MP
Hymel
L J
LJ
Mason
M J
MJ
D000818:Animals; D001464:Barium / Q000378:metabolism / Q000493:pharmacokinetics; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D002463:Cell Membrane Permeability / Q000502:physiology; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D008214:Lymphocytes / Q000378:metabolism* / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008345:Manganese / Q000378:metabolism / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000502:physiology*; D009532:Nickel / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D013950:Thymus Gland / Q000166:cytology* / Q000502:physiology
D007211:Indoles; D015221:Potassium Channels; D013729:Terpenes; D001464:Barium; D008345:Manganese; D004533:Egtazic Acid; D015759:Ionomycin; D019284:Thapsigargin; D009532:Nickel; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium; C000543:cyclopiazonic acid