Ionomycin and 2,5'-di(tertbutyl)-1,4,-benzohydroquinone elicit Ca super(2+)-induced Ca super(2+) release from intracellular pools in Physarum polycephalum

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Molecular & integrative physiology, 2001-02, Vol.128 (2), p.279-288
• Main Authors: Kochegarov, A A, Beylina, SI, Matveeva, N B, Leontieva, G A, Zinchenko, V P
• Format: Article
• Language: English
• Subjects: 2,5'-Di(tertbutyl)-1,4,-benzohydroquinone; Ionomycin; Physarum polycephalum; Procaine; ryanodine; ryanodine receptors
• ISSN: 1095-6433

Calcium level in organelles of the slime mold Physarum polycephalum was monitored by chlortetracycline, a low-affinity calcium indicator. It was found that 2,5'-di(tertbutyl)-1,4,-benzohydroquinone (BHQ) at a concentration of 100 mu M, but not the highly specific inhibitor of sarco-endoplasmic reticulum Ca super(2+)-ATPase (SERCA), thapsigargin (1-10 mu M), elicited calcium release from the CTC-stained intracellular calcium pool. Ionomycin also caused a calcium release (23.7 plus or minus 5.1%), which was less than that induced by BHQ (30.1 plus or minus 6.0%). Procaine (10 mM), a blocker of ryanodine receptor, completely abolished the responses to BHQ and ionomycin. Another blocker, ryanodine (100 mu M), only slightly diminished the responses to ionomycin and BHQ. Apparently, BHQ and ionomycin acting as a Ca super(2+)-ATPase inhibitor and an ionophore, respectively, elicit an increase in [Ca super(2+)] sub(i), which in turn triggers a calcium-induced calcium release (CICR) via the ryanodine receptor. Caffeine, an activator of ryanodine receptor, at a concentration of 25-50 mM produced a Ca super(2+)-release (5.6-16.0%), which was not similar in magnitude to CICR. The response to 25 mM caffeine was only moderately inhibited by 25 mM procaine, and almost completely abolished by 50 mM procaine and 100 mu M ryanodine.