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Differential susceptibility of cholinergic and noncholinergic neurogenic responses to calcium channel blockers and low Ca 2+ medium in rat urinary bladder
Author(s) -
Bhat M.B.,
Mishra S.K.,
Raviprakash V.
Publication year - 1989
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.1476-5381.1989.tb11892.x
Subject(s) - diltiazem , cholinergic , verapamil , calcium channel , calcium , chemistry , endocrinology , channel blocker , voltage dependent calcium channel , medicine , stimulation , neurotransmitter , acetylcholine , biology , central nervous system
1 The influence of calcium channel blockers and low Ca 2+ medium on the neurogenic responses to single pulse electric field stimulation in rat urinary bladder has been examined. 2 Single pulse stimulation evoked a biphasic contractile response consisting of a fast component with a time to peak of 0.72 ± 0.05 s and a slow component that reached a maximal tension at 2.8 ± 0.21 s, possibly mediated by two different neurotransmitters. 3 Atropine (3 × 10 −6 m ) selectively inhibited the slow component without altering the fast component, suggesting the involvement of cholinergic and non‐cholinergic neurotransmitters, respectively. 4 Reducing Ca 2+ in the medium to 1/4 of the normal, abolished the slow component of the neurogenic response while the fast contractile response was not altered which may indicate a relatively greater dependence of the cholinergic component on extracellular Ca 2+ than the noncholinergic one. 5 The IC 50 values for the fast component with respect to verapamil and diltiazem were 1.08 μ m and 1.76 μ m , respectively. The greater susceptibility of the slow component to calcium channel blockers (IC 50 values of verapamil: 0.07 μ m and of diltiazem: 0.25 μ m ) indicates the differential activation of slow calcium channels by the endogenously released substances. 6 Calcium channel blockers inhibited the ATP‐induced contraction which was comparable to that of the non‐cholinergic component of the neurogenic response suggesting the involvement of ATP as a possible neurotransmitter. 7 ACh‐induced contractions were relatively less susceptible to calcium channel blockers and low Ca 2+ medium than was the atropine‐sensitive cholinergic component of the neurogenic response.