| 8842521 |
Li G, Wollheim CB, Pralong WF: Oscillations of cytosolic free calcium in bombesin-stimulated HIT-T15 cells. Cell Calcium. 1996 Jun;19(6):535-46.
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. |
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