Transmembrane ionic currents in smooth muscle of the pulmonary artery

Buryi, V. A.; Gurkovskaya, A. V.

doi:10.1007/bf00834068

Cited by 1 publication

(1 citation statement)

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“…These actions of catecholamines are thought to be mediated by stimulation of a-receptors (Bulbring & Tomita 1969a, b, Jenkinson & Morton 1967 a, b ) . It seems now to be widely accepted that the inward current during action potential discharge in smooth muscle can be carried by Ca2+ (Brading et al 1969, Vassort 1976, Inomata & Kao 1976, Bury & Shuba 1976, Fleckenstein 1977. If sufficient amounts of Ca2+ was carried by action potentials to cause contraction of the intestine, as suggested to be the case in the guinea pig urethra (Bury & Shuba 1976), it would be rather simple to explain the relaxation on a receptor stimulation by assuming that the cessation of action potential discharge diminished entrance of extracellular calcium.…”

Section: Relationship Between Stimulation Of Ai Receptors and Smooth mentioning

confidence: 99%

Reversal of α₁‐receptor mediated relaxation in intestinal smooth muscle

Wikberg

1981

Acta Physiologica Scandinavica

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The alpha 1-receptor agonist phenylephrine relaxed longitudinal rabbit jejunal muscle contracted in vitro by low concentrations of barium ions (1 mM). When the Ba2+ concentration was increased to 10-15 mM the response to phenylephrine was a contraction, and at Ba2+ concentrations in between the high and low range this response was biphasic--a relaxation followed by a contractile phase. The alpha 2-receptor agonist clonidine did not affect the tone of the Ba2+ contracted preparation. When the muscle preparation was contracted by Sr2+ (1-20 mM) in the presence of Ca2+ (2.5 mM), phenylephrine relaxed it, and no contractile response to phenylephrine was observed. In the absence of extracellular Ca2+, 5 mM Ba2+ caused a contraction. Under these conditions phenylephrine had no effect on the tissue tone. When Ca2+ was added in a low concentration (0.2-2 mM), phenylephrine elicited a gradually increasing contractile response. At 5 mM Ca2+ the contractile response was replaced by the normal relaxation. The contractile response to phenylephrine in the presence of 5 mM Ba2+ and 2.5 mM Ca2+ was partially blocked by low concentrations of verapamil. In higher concentrations verapamil abolished the tissue tonus completely. The contractile response to phenylephrine in the presence of 5 mM Ba2+ and 2.5 mM Ca2+ could be reverted to the normal relaxation by the addition of 20 mM Mg2+. Increasing the K+ concentration from the normal 5.9 to 62.9 mM blocked the phenylephrine-induced relaxation. No contractile response to phenylephrine occurred. It is concluded that Ba2+ could reverse the response of alpha 1 receptor stimulation in rabbit jejunum from a relaxation to a contraction and that this contractile response was dependent on the presence of Ca2+.

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Section: Relationship Between Stimulation Of Ai Receptors and Smooth mentioning

confidence: 99%