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H Banno

Publications and source records attributed to H Banno.

22 records · Page 2Linked to original sources
PubMed1987

Cellular mechanisms of supersensitivity to acetylcholine and potassium ion after ciliary ganglionectomy in the rat iris sphincter muscle.

The effect of parasympathectomy on the electrical and nonelectrical activation of iris smooth muscle cells was examined 7-10 days after ciliary ganglionectomy in order to explore the mechanisms involved in the nonspecific denervation supersensitivity. Resting membrane potential of rat iris sphincter muscle cells was not altered by cholinergic denervation. Although the degree of depolarization induced by raising [K]o was little affected by denervation, K-contracture was always potentiated. Acetylcholine (ACh) never modified membrane potential in normal iris muscles even at a high concentration of 50 microM. After denervation, ACh produced a much larger contraction, and at higher concentrations, concomitantly produced a depolarization which was far too small to account for the enhanced contraction. There were 3- and 4.6-fold increases in sensitivity to Ca and Sr, respectively, in the contractile response in high-K, Ca-free solution after denervation. The response to Ca was greatly enhanced also in height, and a large part of the increment of the response to 2 mM Ca was suppressed by 0.1 microM nifedipine. In the depolarized muscle of normal irides, Mn ion had two distinct effects, a calcium blocking effect at lower concentrations (less than or equal to 1.2 mM) and a contractile effect at higher concentrations (greater than or equal to 1.8 mM). Denervation caused a marked increase in the contractile effect of Mn (greater than or equal to 0.6 mM). ACh elicited phasic contraction only once in the absence of external Ca. This response was much enhanced by parasympathectomy. Fluoride ion (F) also produced a distinct contraction many times in the Ca-free solution. F-induced contraction was much larger in denervated muscle than in normal muscle. These results indicate that denervation of the rat iris sphincter muscle does not significantly affect the electrical property of the muscle cells, and suggest that denervation may increase Ca-influx of the cell membrane, may increase the amount of releasable Ca from an intracellular store site, and might increase the functional activity of the contractile protein.

Acetylcholine↗
PubMed1985

Pharmaco-mechanical coupling in the response to acetylcholine and substance P in the smooth muscle of the rat iris sphincter.

In the rat iris sphincter muscle contractile responses to transmural stimulation consisted of two components, a fast cholinergic followed by a slow non-adrenergic, non-cholinergic (NANC) one. The magnitude of the latter varied widely and was on average 5% of that of the cholinergic component. Exogenous substance P (1 nM-1 microM) produced a concentration-dependent contraction, the maximum amplitude of which was as large as that produced by acetylcholine (ACh). Capsaicin (10 microM) induced a transient contraction only once in each preparation. After the treatment with capsaicin the NANC component disappeared. Neither nerve nor direct electrical stimulation with short pulses elicited any active change in the membrane potential under physiological conditions, but an action potential was triggered by direct stimulation when the extracellular Ca ion was totally replaced by Ba ion. Under the latter conditions spontaneous spike potentials occurred repetitively. ACh and substance P produced a large contraction without modifying the membrane potential. This was also the case in the presence of 5 mM Ba. These results suggest that substance P-ergic innervation may have a far lesser physiological significance than that which has been described in rabbits and that pure pharmaco-mechanical coupling is characteristic of the responses to acetylcholine, substance P, and nerve stimulation in the rat iris sphincter muscle.

Acetylcholine↗
PubMed1984

Anomalous stabilizing action of Ca on sphincter smooth muscle of the rat iris.

This paper concerns the first measurement of spontaneous electrical activity in the smooth muscle cells of the mammalian iris sphincter. Although the membrane potential was quite stable, at - 59 mV, under physiological conditions in vitro, bursts of rhythmic electrical activity occurred when barium was substituted for all of the calcium in the medium (Ba-Krebs' solution). These bursts consisted initially of spike potentials, but these were followed by a long-lasting depolarization. Although the amplitude of the spike potentials did not decrease even when the external Na concentration was lowered to 25 mM, addition of a small amount of Ca (greater than 0.3 mM) to the Ba-Krebs' depressed the rhythmic contractions which followed the cessation of the spike potentials. Strontium also depressed the rhythmicity but to a lesser extent. These results show that the smooth muscle of the rat iris sphincter has an ability to generate spike potentials, and that the properties of the latter differ from those observed in other smooth muscles; i.e. the activity is suppressed by Ca ions at far lower concentrations than those in the physiological environment. This anomalous effect is presumably due to the stabilizing action of Ca.

Action Potentials↗