1. Intracellular recordings from single smooth muscle cells of the guinea-pig vas deferens have been made after depletion of neuronal stores of noradrenaline by chronic reserpine treatment.2. Junctional responses to postganglionic hypogastric nerve stimulation were depressed, but large excitatory junction potentials (EJPs) and action potentials could still be evoked by stimulation at 1-2 c/s.3. These junctional responses were not reduced by the presence of hyoscine (5 x 10(-7) g/ml.), but were greatly depressed by the presence of bretylium (2 x 10(-6) g/ml.).4. Even in the presence of bretylium, junctional responses leading to action potentials could still be evoked by using high voltages of stimulation.5. It is concluded that when neuronal noradrenaline stores have been depleted by reserpine some noradrenaline is still available for release by nerve stimulation.6. It is further concluded that if the non-adrenergic component of the response of the guinea-pig vas deferens to nerve stimulation is cholinergic, this component is resistant to blockade by hyoscine.

Action Potentials↗

PubMed1969

Indirect cholinergic vasomotor control of intestinal blood flow in the domestic chicken.

1. A histochemical and pharmacological study has been made of the relationship between the medial circular and adventitial longitudinal smooth muscle coats of the anterior mesenteric artery of the domestic chicken.2. The longitudinal (LM) coat was found to be innervated by excitatory cholinergic and inhibitory adrenergic nerves, confirming previous reports.3. The circular (CM) coat was found to be innervated by adrenergic vasoconstrictor nerves. There was no evidence for the existence of cholinergic nerves supplying the circular muscle.4. Contraction of the LM had little effect on the resting perfusion pressure of the isolated artery, but caused potentiation of perfusion pressure responses to vasoconstrictor stimuli directly affecting the CM.5. It is suggested that the function of the LM is to modulate the reactivity of the anterior mesenteric artery to vasomotor stimuli, and that this may be particularly implicated in the cardiovascular response to sudden stress.

Acetylcholine↗

PubMed1969

Transmission from vasoconstrictor and vasodilator nerves to single smooth muscle cells of the guinea-pig uterine artery.

1. Previous studies have shown that perivascular nerve stimulation of the uterine artery of the guinea-pig evokes an adrenergic constrictor response and a dilator response with two components. The first of these, only present during pregnancy, is cholinergic. The second is non-cholinergic and is present at all times. Intracellular recording from single smooth muscle cells in isolated arterial segments has now been used to investigate the transmission processes associated with these responses.2. The mean resting membrane potential of the muscle cells was 60.7 mV in arteries from both virgin animals (range 50-68 mV) and from animals in late pregnancy (range 48-76 mV).3. Low frequency perivascular stimulation evoked excitatory junction potentials (EJPs) which reached a maximum amplitude of about 5 mV, lasted about 900-1000 msec, and showed facilitation at frequencies of stimulation of 0.1 Hz or above and summation at frequencies of stimulation of 1.2 Hz or above.4. These EJPs were abolished by exposure of the tissue to bretylium (2 x 10(-6) g/ml.). It is therefore concluded that the EJPs were due to transmission from adrenergic nerves.5. Perivascular stimulation at frequencies above 10 Hz evoked a depolarizing response which was often surmounted by a small (5 mV) local spike potential. Such depolarizing responses were associated only with localized contractions of the arterial muscle.6. In the presence of low extracellular K(+) concentrations, perivascular stimulation at frequencies above 10 Hz gave rise to a depolarizing response topped by an action potential of up to 50 mV amplitude, and more generalized contraction of the tissue than was seen in normal K(+) solution.7. After blockade of the adrenergic vasoconstrictor fibres, no response to perivascular stimulation was observed normally. However, following moderate depolarization of the membrane with noradrenaline, stimulation evoked a hyperpolarization of up to 6 mV in amplitude.8. This response showed no discrete junction potentials, had a latency of up to 2000 msec and was only observed with stimulation at frequencies of 2 Hz or greater. The response was obtained in both pregnant and non-pregnant animals, and was unaffected by hyoscine, but was abolished by cinchocaine.9. No changes in membrane potential attributable to transmission from cholinergic dilator nerves could be revealed in arteries from pregnant animals. Furthermore, high concentrations of acetylcholine had no polarizing effect on the muscle cells. It is suggested that the cholinergic dilator nerves may not act via changes in membrane potential.

Acetylcholine↗

PubMed1969