Hikaru Suzuki

Acetylcholine releases endothelium-derived hyperpolarizing factor and EDRF from rat blood vessels.

1 The effects of haemoglobin and methylene blue on the acetylcholine (ACh)‐induced electrical and mechanical responses of smooth muscle cells were investigated in rat aorta and rat main pulmonary artery. 2 When the endothelium was intact, ACh induced a transient hyperpolarization and sustained relaxation of tissues precontracted with noradrenaline. Both hyperpolarization and relaxation were absent in preparations without endothelium. 3 Haemoglobin and methylene blue inhibited the ACh‐induced relaxation, but not the transient hyperpolarization. 4 In aorta with an intact endothelium, ACh produced an increase in both the rate of 86Rb efflux and tissue cyclic GMP levels. The changes in ion flux were unaffected by either haemoglobin or methylene blue in concentrations which almost abolished the increase in cyclic GMP concentrations. 5 In arteries with an intact endothelium, indomethacin had no effect on the ACh‐induced electrical and mechanical responses or on the increase in 86Rb efflux and tissue cyclic GMP levels. 6 It is concluded that in the rat aorta and rat main pulmonary artery, ACh releases two different substances, an endothelium‐derived relaxing factor (EDRF) and a hyperpolarizing factor (EDHF), from the endothelial cells. Neither substance appears to be derived from a pathway dependent on cyclo‐oxygenase. EDHF seems to play a minor role in the relaxation of noradrenaline‐induced contractions.

Excitation—contraction coupling in smooth muscle cells of the guinea-pig mesenteric artery

1. The excitation—contraction coupling mechanism in the smooth muscle of the guinea‐pig mesenteric artery was studied using intact and chemically skinned muscle cells.

Some electrical properties of the endothelium‐dependent hyperpolarization recorded from rat arterial smooth muscle cells.

1. Electrical responses produced by acetylcholine (ACh) and histamine were recorded from smooth muscle cells of the intralobular small pulmonary artery (SPA), main pulmonary artery (MPA) and thoracic aorta of rats. 2. In MPA and SPA, ACh and histamine produced a transient hyperpolarization of the membrane, and the potential decayed exponentially with a time constant of 2‐3 min. In aorta, ACh produced a sustained and histamine produced a transient hyperpolarization. 3. The ACh‐ and histamine‐induced hyperpolarizations were blocked by atropine and mepyramine, respectively, or by removing the endothelial cells. 4. The amplitude of the hyperpolarization was increased in low [K+]o solutions and decreased in high [K+]o solutions. The ionic conductance of the membrane was increased during the hyperpolarization, suggesting an involvement of the increased potassium conductance. 5. A reproducible amplitude of hyperpolarization was generated when ACh or histamine was applied at intervals of over 10 or 30 min, respectively. 6. In aorta, after the transient hyperpolarization had ceased during continued application of histamine, ACh again produced a hyperpolarization, i.e. the transient nature of the hyperpolarization was not due to desensitization of the receptor upon which the hyperpolarizing substance acted, assuming histamine and ACh release the same hyperpolarizing substance. 7. ACh and histamine relaxed the tissues from SPA, MPA and aorta during the noradrenaline (NA)‐ or high [K+]o solution‐induced contraction, in a concentration‐dependent manner, only when the endothelial cells were intact. Both ACh and histamine were potent relaxants in MPA and aorta, but showed weak relaxing actions in SPA. 8. In aorta, ACh and histamine produced a sustained relaxation for up to 10 min, and Methylene Blue diminished and altered it to a transient relaxation (for histamine) or an initial large, followed by a small sustained (for ACh), relaxation. 9. In the presence of NA and NA plus Methylene Blue, ACh and histamine also produced a hyperpolarization similar to that seen in the control. 10. It is concluded that in arteries of the rat, ACh and histamine release a hyperpolarizing substance from the endothelial cells. This substance may be different from the endothelium‐derived relaxing factor (EDRF), and is released mainly transiently. The hyperpolarization is generated by an increase in potassium conductance of the membrane, and this has some contribution to the endothelium‐dependent relaxation.

Calcium dependency of the endothelium-dependent hyperpolarization in smooth muscle cells of the rabbit carotid artery.

1. In smooth muscle cells of the rabbit carotid artery, ACh (greater than 10(‐8) M) generated a hyperpolarization with two components (transient followed by sustained), only in the tissues with an intact endothelium. There were no detectable changes in the membrane potential, as elicited by ACh (up to 10(‐5) M) in tissues with no endothelium or in the presence of atropine (10(‐6) M). 2. Reduction of [Ca2+]o inhibited the sustained component which was not apparent in [Ca2+]o below 0.16 mM. In Ca2+‐free (EGTA‐containing) solution, the generation of the transient component of the hyperpolarization remained sustained but with a substantially reduced amplitude. 3. Procaine (greater than 10(‐6) M) inhibited the ACh‐induced hyperpolarization in a concentration‐dependent manner, and at a concentration of procaine (10(‐3) M) which caused substantial depolarization of the membrane, no detectable change was elicited by ACh. 4. Caffeine (10(‐6)‐10(‐3) M) produced a transient hyperpolarization, independent of the presence or absence of the endothelium, and inhibited the sustained component of the ACh‐induced hyperpolarization more so than the initial component. 5. A23187 (greater than 10(‐8) M) hyperpolarized the smooth muscle membrane in a concentration‐dependent manner, and this hyperpolarization was not generated in Ca2+‐free solution or in the absence of endothelial cells. 6. In intact tissues, pre‐treatment with A23187 resulted in a reduction of the subsequently generated ACh‐induced hyperpolarization, in an irreversible manner. 7. It would thus appear that in the rabbit carotid artery, the endothelium‐dependent hyperpolarization induced by ACh has Ca2+‐dependent and Ca2+‐independent components, and each may be related to the increase in endothelial [Ca2+]i by release from the intracellular store and by influx from the extracellular medium, respectively. The increased [Ca2+]i would trigger a release of an endothelium‐derived hyperpolarizing factor (EDHF) from the endothelial cells.

The membrane properties of the smooth muscle cells of the rabbit main pulmonary artery

1. The membrane potential of the smooth muscle cells of the rabbit main pulmonary artery amounts to ‐57 mV, the length constant of the tissue is 1·48 mm and the time constant of the membrane 182 msec. On the basis of the electrical properties of its membrane, this smooth muscle tissue is classified as a single‐unit type. During outward current pulses, the membrane shows marked rectification and action potentials can never be generated.

Excitation—contraction coupling in the smooth muscle cells of the rabbit main pulmonary artery

1. Increasing the external K concentration depolarizes the smooth muscle cells of the main pulmonary artery, and this depolarization reaches a maximal slope of 58 mV for a tenfold change of [K]o. The threshold depolarization for inducing contraction is at 4 mV and the maximal contraction is reached at a [K]o of 58 m M.

Differences and similarities in the noradrenaline‐ and caffeine‐induced mechanical responses in the rabbit mesenteric artery

1. The properties of noradrenaline (NA)‐induced and caffeine‐induced contractions in the rabbit mesenteric artery were investigated and compared, using intact and skinned muscles.

Antennal movements induced by odour and central projection of the antennal neurones in the honey-bee

Abstract Movements of the antennae induced by odour were investigated. Odour presented to the antenna of one side induced both antennae to move to that side. The EMGs recorded from the flexor muscles of both scapes showed that the latency of the movement of the ipsilateral flagellum when induced by odour was about 71 msec shorter than that of the contralateral flagellum. Recording electrical activities from the antennal nerve showed that there are more than 14 neurones in the antenno-motor externus. The distribution of the antennal nerve in the brain was investigated histologically by the injection of fluorescent dye. Antennal sensory neurones terminated at the glomeruli in the antennal lobe, in the dorsal lobe, in the protocerebrum, and in the commissural part of the suboesophageal ganglion. Injection of the fluorescent dye into the antennal nerve after degeneration of the antennal sensory neurones showed that the antennal motoneurones run in the ventral side of the antennal and dorsal lobes, and terminate in the marginal region of the ipsilateral oesophageal connective. The difference in latency of odour-induced flagellar movements is discussed in relation to the histological results and the unitary responses in the brain reported previously.

The effects of acetylcholine on the membrane and contractile properties of smooth muscle cells of the rabbit superior mesenteric artery.

1 Effects of acetylcholine (ACh) on the membrane potential and mechanical properties of rabbit superior mesenteric artery were investigated by the use of microelectrode and isometric tension recording methods. The membrane potential was −62.5 ± 3.0 mV (s.d.). The maximum slope of the membrane depolarization produced by tenfold increase in [K]0 plotted on a log scale was 48 mV. Excess [K]0 and low [K]0 depolarized the membrane and produced contraction (contracture). The minimum depolarization to produce contraction was 10 mV. 2 Low concentrations (10 and 100 ng/ml) of ACh hyperpolarized the membrane. Increased concentrations of ACh (1 and 10 μg/ml) hyperpolarized the membrane further in adult rabbit, while increased concentrations of ACh produced a smaller hyperpolarization in young rabbit. These potential changes produced by ACh in immature and adult rabbits were suppressed by treatment with atropine (0.1 μg/ml). 3 ACh (10 ng to 1 μg/ml) consistently generated contraction in Krebs solution. However, ACh relaxed the contraction induced by either K+ or noradrenaline in the adult rabbit, and it enhanced contraction produced by this treatment in the immature rabbit. In Ca‐free EGTA solution, the action of ACh on the mechanical response was markedly suppressed, although high concentrations of ACh still evoked contraction. However, treatment with atropine (1 μg/ml) completely prevented these actions of ACh. 4 ACh‐induced relaxation during either K+‐induced or noradrenaline‐induced contraction was not caused by the hyperpolarization of the membrane. 5 It is concluded that ACh possesses dual actions on smooth muscle cells of the rabbit superior mesenteric artery in Krebs solution, i.e. ACh hyperpolarizes the membrane, while it consistently generates contraction. These ACh actions on the muscle cells were modified by aging.

Effects of endogenous and exogenous noradrenaline on the smooth muscle of guinea‐pig mesenteric vein

Membrane responses of smooth muscles of the guinea‐pig mesenteric vein to noradrenaline released from perivascular nerves or applied exogenously were investigated.