1. The effects of transmural nerve stimulation were examined on prepar
ations of detrusor smooth muscle from guinea-pig urinary bladder using
intracellular recording techniques. Most recordings were made from pr
eparations in which spontaneous and evoked action potentials had been
inhibited by nifedipine (10 mu M), a dihydropyridine that blocks L-typ
e Ca2+ channels. 2. Supramaximal stimuli evoked excitatory junction po
tentials (EJPs) which could be divided into three basic types. Type 1
EJPs had short latencies (<30 ms) and fast rise times (<60 ms). Type 2
EJPs consisted of two components: a small depolarization that was fol
lowed by a second depolarization with a faster rise time. In a third t
ype of cell, at high strengths of stimulation, EJPs resembled type 1 E
JPs but at lower strengths of stimulation were similar in time course
to type 2 EJPs. 3. All EJPs were abolished by tetrodotoxin (1 mu M) an
d reduced by omega-conotoxin (0.1 mu M), but were unaffected by hexame
thonium (0.1 mM), suggesting that they result from the release of tran
smitter from post-ganglionic nerve fibres. All responses persisted in
the presence of atropine (1 mu M) but were abolished following the des
ensitization of P-2-purinoceptors with alpha,beta-methylene ATP (m-ATP
; 10 mu M). 4. Spontaneous excitatory junction potentials (SEJPs) were
also recorded fr om most cells SEJPs were similar in appearance to fa
st single-component EJPs; however, in general they had a briefer time
course. SEJPs persisted in the presence of tetrodotoxin (1 mu M). 5. T
he electrical proper ties of urinary bladder smooth muscle were also e
xamined. Voltage changes induced by point current injection into cells
had fast rates of rise and decay (time constant, 5-20 ms). The input
resistance of cells ranged between 12 and 108 M Omega. When recordings
were taken from cells near the point of current injection, resultant
electrotonic potentials could be detected in only a small proportion o
f cells. 6. The results are discussed in relation to the idea that tra
nsmural nerve stimulation in the guinea-pig urinary bladder causes the
activation of at least two different membrane conductances. Cells app
ear to be electrically coupled with one another. However, it is likely
that coupling exists within discrete bundles of the smooth muscle.