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Elementary purinergic Ca 2 + transients evoked by nerve stimulation in rat urinary bladder smooth muscle
Author(s) -
Heppner Thomas J.,
Bonev Adrian D.,
Nelson Mark T.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.077826
Subject(s) - purinergic receptor , suramin , muscarinic acetylcholine receptor , chemistry , stimulation , ppads , endocrinology , tetrodotoxin , medicine , agonist , biophysics , voltage dependent calcium channel , receptor , calcium , biology , biochemistry
The translation of nerve transmission to Ca 2 + signals in urinary bladder smooth muscle (UBSM) is incompletely understood. Thus, we sought to characterize Ca 2 + signals in strips of UBSM loaded with the Ca 2 + ‐sensitive fluorescent dye, fluo‐4, using laser scanning confocal microscopy. Two types of Ca 2 + signals occurred spontaneously and could be evoked with field stimulation: large, rapid, global Ca 2 + transients termed ‘global Ca 2 + flashes’, and much smaller, localized Ca 2 + transients. Global Ca 2 + flashes were inhibited by the L‐type voltage‐dependent Ca 2 + channel (VDCC) inhibitor, diltiazem and with P2X receptor blockade. Simultaneous intracellular recordings and Ca 2 + measurements indicated that these events are caused by Ca 2 + influx through VDCCs during action potentials. Small, local Ca 2 + transients occurred spontaneously, and their frequency could be elevated with field stimulation. Atropine, an inhibitor of muscarinic receptors, did not affect these local Ca 2 + transients. However, the desensitizing P2X receptor agonist α,β‐methylene ATP, and the purinergic antagonist, suramin, effectively inhibited the local Ca 2 + transients. The frequency of these ‘purinergic Ca 2 + transients’ was increased about 7‐fold by a 10 s stimulus train (1 Hz). The amplitude, duration at one‐half amplitude and the spatial spread of the evoked purinergic Ca 2 + transients were F / F o = 2.4 ± 0.13, 111.7 ± 9.3 ms and 14.0 ± 1.0 μm 2 , respectively. Tetrodotoxin inhibited evoked purinergic Ca 2 + transients, indicating that they were dependent on nerve fibre activation. Purinergic Ca 2 + transients were not dependent on VDCC activity. Neither 2‐APB, an inhibitor of inositol 1,4,5‐triphosphate (Ins(1,4,5)P 3 ) (IP 3 )‐induced Ca 2 + release, nor ryanodine inhibited the purinergic Ca 2 + transients. We have identified two novel Ca 2 + signals in rat UBSM. Large, rapid, global Ca 2 + flashes that represent Ca 2 + influx through VDCCs during action potentials, and local, purinergic Ca 2 + transients that represent Ca 2 + entry through P2X receptors. Our results indicate that purinergic Ca 2 + transients evoked by release of ATP from nerve varicosities are elementary signals in the process of nerve‐smooth muscle communication.