Electrical and mechanical responses of guinea‐pig bladder muscle to nerve stimulation

Abstract

1 The electrical and mechanical responses to transmural stimulation of intrinsic nerves have been recorded from smooth muscle strips dissected from the dome of the guinea-pig bladder, by use of intracellular microelectrodes, and conventional tension recording techniques. 2 Stimulation of intrinsic nerves evoked action potentials in all cells studied. Hyperpolarization of the cells by extracellular current injection revealed subthreshold excitatory junction potentials (ej.ps) in about a quarter of the cells studied. 3 Action potentials could still be evoked in the presence of atropine and neostigmine, but were abolished after desensitization of the cells to a,#-methylene ATP, a stable analogue of ATP.4 In the presence of neostigmine, the evoked action potential was followed by a slow depolarization of the membrane. The mechanical response increased in amplitude and duration. 5 The contractile response to transmural nerve stimulation was reduced but not abolished in the presence of either atropine or desensitizing doses of a,fi-methylene ATP. Atropine was more effective at high frequencies of stimulation () 30Hz), and a,#-methylene ATP at low frequencies ( < 15 Hz). In combination the drugs abolished the response. 6 The results suggest that the mechanical response to excitatory nerve stimulation is biphasic. The early transient reponse is elicited by ej.ps and evoked spikes, is resistant to atropine, but sensitive to desensitization of purinoceptors. The late response is mediated through muscarinic receptors, involves little membrane depolarization, and is unaffected by desensitization of purinoceptors. These responses are analogous to the responses seen in rabbit bladder, and in the sympathetically innervated rat tail artery and guinea-pig vas deferens.

The effect of in vivo oestrogen pretreatment on the contractile response of rat isolated detrusor muscle

“…Brading & Williams (1990) have clearly shown that the predominant mechanical response to intrinsic nerve stimulation of rat and guinea-pig detrusor was through non-muscarinic receptors and that contractile responses resistant to atropine are most clearly seen in the early response to electrical field stimulation. Conversely neostigmine (Brading & Mostwin, 1989) and physostigmine potentiated electrical field stimulation at low although less than at high frequencies. There is now good evidence that the non-cholinergic transmitter is adenosine 5'-triphosphate (ATP) (Brading & Mostwin, 1989;Brading & Williams, 1990;Parija et al, 1991), but whether pretreatment affects this mechanism is unknown at present.…”

“…Conversely neostigmine (Brading & Mostwin, 1989) and physostigmine potentiated electrical field stimulation at low although less than at high frequencies. There is now good evidence that the non-cholinergic transmitter is adenosine 5'-triphosphate (ATP) (Brading & Mostwin, 1989;Brading & Williams, 1990;Parija et al, 1991), but whether pretreatment affects this mechanism is unknown at present.…”

Modulation of Purinergic Neuromuscular Transmission by Phorbol Dibutyrate is Independent of Protein Kinase C in Murine Urinary Bladder

“…Recordings of electrically evoked EJPs from smooth muscle cells of the rabbit urinary bladder detrusor muscle (using both microelectrode and sucrose gap methods) were first published by Creed et al, (1983). Later work demonstrated that the atropine-resistant EJPs recorded in the bladders of rabbits, guinea-pigs, and pigs were inhibited by desensitization of the ATP receptor with ␣,␤-methylene ATP (Hoyle and Burnstock, 1985;Hashitani and Suzuki, 1995;Fujii, 1988;Brading and Mostwin, 1989;Bramich and Brading, 1996). In other studies, high concentrations of the purinergic antagonist suramin were found to reduce the amplitude of EJPs recorded by the sucrose gap method in rabbit and guinea-pig bladder (Creed et al, 1994).…”

A survey of commonalities relevant to function and dysfunction in pelvic and sexual organs

“…25,58 In the presence of L-type Ca channel blockers, ejps can still be evoked, but there is little contractile response. The ejps are not blocked by atropine, but are blocked by desensitization of the P2x purinoceptors.…”