Ionomycin, a Ca++ ionophore, increases platelet volume independently of the Na+/H+ exchanger.
A Ca++-ionophore, ionomycin, increased the volume of human platelets suspended in a Ca++-containing buffer. This change in cell volume was dependent upon ionomycin and extracellular Ca++ concentrations, suggesting that the volume change occurs when the intracellular Ca++ reaches a certain level (greater than uM as determined by aequorin method). The ionomycin-induced volume increase was suppressed by replacement of extracellular Na+ with membrane-impermeable N-methyl-D-glucamine or Cs+, but not with Li+, K+, or Rb+. Ethylisopropylamiloride, a potent inhibitor of the Na+/H+ exchanger, had only weak inhibitory effect, and the apparent Km for Na+ was approximately 350 mM, which is much larger than that of the Na+/H+ exchanger. It is suggested that certain mechanisms other than the Na+/H+ exchanger are responsible for ionomycin-induced volume increase.
Ozaki
Y
Y
Department of Clinical and Laboratory Medicine, Yamanashi Medical College, Japan.
Matsumoto
Y
Y
Yatomi
Y
Y
Higashihara
M
M
Kariya
T
T
Kume
S
S
D001792:Blood Platelets / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D002118:Calcium