M. Oike et al., INCREASE IN CALCIUM IN SMOOTH-MUSCLE CELLS OF THE RABBIT BLADDER INDUCED BY ACETYLCHOLINE AND ATP, Journal of the autonomic nervous system, 69(2-3), 1998, pp. 141-147
Cultured smooth muscle cells from rabbit urinary bladder were loaded w
ith fura-2. Changes in intracellular Ca concentration [Ca-i(2+]) produ
ced by acetylcholine (ACh) or adenosine triphosphate (ATP) were estima
ted by measuring the fluorescence ratio F340/F380. Western blot analys
is and immunohistochemical techniques showed that the cultured cells r
etained alpha-smooth muscle actin. ATP produced a rapid but transient
increase in [Ca2+](i) and ACh produced a delayed, prolonged increase.
Application of ACh after ATP in Ca-free solution failed to elevate [Ca
2+](i) suggesting that both ACh and ATP release Ca2+ from the same int
racellular stores. Following application of ACh but not ATP in Ca-free
Krebs solution, reintroduction of Ca2+ produced elevation of [Ca2+](i
), indicating that ACh causes prolonged opening of channels in the mem
brane. The sustained increase induced by ACh was abolished by nicardip
ine (blocker of Ca2+ voltage dependent channel I-Ca(V)) or quinine (bl
ocker of non-selective cation channels). Although the elevations to AC
h or ATP were abolished by neomycin (an inhibitor of phospholipase C)
the different time courses suggest that the mechanisms of release of C
a2+ from intracellular stores or the pathway for refilling the stores
is different. (C) 1998 Elsevier Science B.V. All rights reserved.