Dual effects of mastoparan on intracellular free Ca2+ concentrations in human astrocytoma cells.
1. The effect of mastoparan, a wasp venom toxin, on intracellular free Ca2+ concentration ([Ca2+]i) was examined in human astrocytoma cells. Mastoparan inhibited [Ca2+]i induced by carbachol (100 microM) in a concentration-dependent manner in the absence of extracellular Ca2+, consistent with our previous results showing that mastoparan inhibits phosphoinositide hydrolysis in human astrocytoma cells. 2. In contrast, mastoparan itself increased [Ca2+]i and augmented carbachol-induced increase in the [Ca2+]i in the presence of extracellular Ca2+, suggesting that mastoparan elicited Ca2+ influx from the extracellular medium. The increase appeared to be maximum at extracellular Ca2+ concentrations of 0.1-0.2 mM. The higher concentrations of extracellular Ca2+ depressed the influx. 3. Pertussis toxin did not affect mastoparan-induced inhibition of [Ca2+]i in the absence of extracellular Ca2+, consistent with the previous results that pertussis toxin did not affect mastoparan-induced inhibition of phosphoinositide hydrolysis. 4. Pertussis toxin augmented mastoparan-induced increase in [Ca2+]i in the presence of extracellular Ca2+, suggesting that pertussis toxin substrate(s) seems to be inhibitory for Ca2+ influx induced by mastoparan. 5. Verapamil, nifedipine and diltiazem (each 10 microM), L-type Ca2+ antagonists, did not affect mastoparan-induced Ca2+ influx. However, verapamil (10 microM) slightly inhibited the increase in [Ca2+]i induced by carbachol in the presence of mastoparan. 6. The results obtained in the present study indicate that mastoparan has two opposite effects on [Ca2+]i in human astrocytoma cells and possibly has at least two sites of action.
Department of Pharmaceutical Molecular Biology, Pharmaceutical Institute, Tohoku University, Sendai, Japan.
N
N
Nakahata
H
H
Ishimoto
K
K
Mizuno
Y
Y
Ohizumi
H
H
Nakanishi
D001254:Astrocytoma / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D016257:Fura-2; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D009423:Nervous System Neoplasms / Q000378:metabolism*; D010455:Peptides; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014862:Wasp Venoms / Q000494:pharmacology*
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; D010716:Phosphatidylinositols; D010566:Virulence Factors, Bordetella; D014862:Wasp Venoms; C037500:mastoparan; D002217:Carbachol; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium; D016257:Fura-2