Oscillations of cytosolic free calcium in bombesin-stimulated HIT-T15 cells.
The mechanism underlying the generation of cytosolic free Ca2+ ([Ca2+]i) oscillations by bombesin, a receptor agonist activating phospholipase C, in insulin secreting HIT-T15 cells was investigated. At 25 microM, 61% of cells displayed [Ca2+]i oscillations with variable patterns. The bombesin-induced [Ca2+]i oscillations could last more than 1 h and glucose was required for maintaining these [Ca2+]i fluctuations. Bombesin-evoked [Ca2+]i oscillations were dependent on extracellular Ca2+ entry and were attenuated by membrane hyperpolarization or by L-type Ca2+ channel blockers. These [Ca2+]i oscillations were apparently not associated with fluctuations in plasma membrane Ca2+ permeability as monitored by the Mn2+ quenching technique. 2,5-di-(tert-butyl)-1,4-benzohydroquinone (tBuBHQ) and 4-chloro-m-cresol, which interfere with intracellular Ca2+ stores, respectively, by inhibiting Ca(2+)-ATPase of endoplasmic reticulum and by affecting Ca(2+)-induced Ca2+ release, disrupted bombesin-induced [Ca2+]i oscillations. 4-chloro-m-cresol raised [Ca2+]i by mobilizing an intracellular Ca2+ pool, an effect not altered by ryanodine. Caffeine exerted complex actions on [Ca2+]i. It raised [Ca2+]i by promoting Ca2+ entry while inhibiting bombesin-elicited [Ca2+]i oscillations. Our results suggest that in bombesin-elicited [Ca2+]i oscillations in HIT-T15 cells: (i) the oscillations originate primarily from intracellular Ca2+ stores; and (ii) the Ca2+ influx required for maintaining the oscillations is in part membrane potential-sensitive and not coordinated with [Ca2+]i oscillations. The interplay between intracellular Ca2+ stores and voltage-sensitive and voltage-insensitive extracellular Ca2+ entry determines the [Ca2+]i oscillations evoked by bombesin.
Li
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G
Division of Clinical Biochemistry, University of Geneva Medical School, Switzerland.
Wollheim
C B
CB
Pralong
W F
WF
D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology; D001839:Bombesin / Q000494:pharmacology*; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002460:Cell Line; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D002940:Circadian Rhythm; D003408:Cresols / Q000494:pharmacology; D006224:Cricetinae; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D016257:Fura-2 / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006873:Hydroquinones / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D012433:Ryanodine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D000697:Central Nervous System Stimulants; D002614:Chelating Agents; D003408:Cresols; D006873:Hydroquinones; D012433:Ryanodine; C019359:2,5-di-tert-butylhydroquinone; C006984:chlorocresol; D002110:Caffeine; D004533:Egtazic Acid; D014700:Verapamil; D000252:Calcium-Transporting ATPases; D005947:Glucose; D003981:Diazoxide; D001839:Bombesin; D002118:Calcium; D016257:Fura-2