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Dual effects of mastoparan on intracellular free Ca 2+ concentrations in human astrocytoma cells
Author(s) -
Nakahata Norimichi,
Ishimoto Hiromi,
Mizuno Kohichi,
Ohizumi Yasushi,
Nakanishi Hironori
Publication year - 1994
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1994.tb13068.x
Subject(s) - mastoparan , extracellular , pertussis toxin , chemistry , phospholipase c , intracellular , biochemistry , endocrinology , biology , g protein , receptor
1 The effect of mastoparan, a wasp venom toxin, on intracellular free Ca 2+ concentration ([Ca 2+ ] i ) was examined in human astrocytoma cells. Mastoparan inhibited [Ca 2+ ] i induced by carbachol (100 μ m ) in a concentration‐dependent manner in the absence of extracellular Ca 2+ , consistent with our previous results showing that mastoparan inhibits phosphoinositide hydrolysis in human astrocytoma cells. 2 In contrast, mastoparan itself increased [Ca 2+ ] i and augmented carbachol‐induced increase in the [Ca 2+ ] i in the presence of extracellular Ca 2+ , suggesting that mastoparan elicited Ca 2+ influx from the extracellular medium. The increase appeared to be maximum at extracellular Ca 2+ concentrations of 0.1–0.2 m m . The higher concentrations of extracellular Ca 2+ depressed the influx. 3 Pertussis toxin did not affect mastoparan‐induced inhibition of [Ca 2+ ] i in the absence of extracellular Ca 2+ , 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 [Ca 2+ ] i in the presence of extracellular Ca 2+ , suggesting that pertussis toxin substrate(s) seems to be inhibitory for Ca 2+ influx induced by mastoparan. 5 Verapamil, nifedipine and diltiazem (each 10 μ m ), L‐type Ca 2+ antagonists, did not affect mastoparan‐induced Ca 2+ influx. However, verapamil (10 μ m ) slightly inhibited the increase in [Ca 2+ ] 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 [Ca 2+ ] i in human astrocytoma cells and possibly has at least two sites of action.