Volume 16, Number 13,
Issue of July 1, 1996
pp. 4155-4161
Copyright ©1996 Society for Neuroscience
Multiple Subtypes of Voltage-Gated Calcium Channel Mediate
Transmitter Release from Parasympathetic Neurons in the Mouse
Bladder
Received Nov. 15, 1995; revised April 18, 1996; accepted April 23, 1996.
Sally A. Waterman
Neurosciences Group, Institute of Molecular Medicine, John
Radcliffe Hospital, Headington, University of Oxford, United Kingdom,
and University Department of Pharmacology, University of Oxford, United
Kingdom
Multiple subtypes of voltage-gated calcium channels are coupled to
transmitter release from central neurons; however, only N-type channels
have been shown to play a role in autonomic neurons. The aim of the
present study was to investigate potential roles for other channel
subtypes in transmitter release from parasympathetic neurons in the
mouse bladder using calcium channel toxins alone and in combination.
Transmitter release was measured indirectly by recording the
contraction of bladder dome strips in response to electrical
stimulation of the neurons by single pulses or trains of 20 pulses at
1-50 Hz.
-Conotoxin-GVIA (GVIA) and
-conotoxin-MVIIC (MVIIC)
inhibited contractions in a concentration-dependent manner, with
IC50 values of ~30 and 200 nM, respectively, at low stimulation frequencies.
-Agatoxin-IVA (agatoxin) alone did not have any significant effect
up to 300 nM. Cumulative addition of the toxins
demonstrated that 300 nM agatoxin had a
significant effect after N-type channels were blocked with 100 nM GVIA. MVIIC (3 µM)
reduced the contraction amplitude further. Testing the toxins on the
cholinergic or purinergic component of the contraction separately
showed that acetylcholine release depends primarily on N-type channels
and, to a lesser extent, on P- and Q-type channels, whereas ATP release
involves predominantly P- and Q-type channels. In conclusion,
parasympathetic neurons in the mouse bladder, like central neurons, use
multiple calcium channel subtypes. Furthermore, the release of the two
main transmitters in these neurons has differing dependencies on the
calcium channel subtypes.
Key words:
acetylcholine;
ATP;
agatoxin;
autonomic;
urinary bladder;
conotoxin;
parasympathetic;
voltage-gated calcium channels