Abstract
The magnitude of the acetylcholine (ACh)-induced contractile response of isolated strips of guinea-pig ileal longitudinal smooth muscle gradually declines during long-term exposure to the cholinergic agent. Nonspecific desensitization also develops. Sodium ions (Na+) are gained by the tissue during the initial minutes of exposure but are later extruded. The decline in the ACh response is less in the presence of ouabain while Na+ gain and retention are enhanced. Loss of sensitivity and gain of Na+ is absent in low Na+ solution. When muscles previously in contact with Ca++-rich solution for 2 hours are transferred to a Ca++-free environment, they undergo a substantial contraction lasting 30 to 60 minutes and gain Na+. However, they do not appear to lose sensitivity to the stimulus afforded by the Ca++-free medium. If ACh is present in the Ca++-free medium, loss of sensitivity to stimulation provided by both ACh and the Ca++-free enviroument is observed except when the bathing medium is low in Na+. The data suggest that the loss of sensitivity during exposure to ACh involves not only accumulation but also extrusion of Na+ by the muscle strips. The results have been interpreted to suggest that the cholinergic agent induces a redistribution of Na+ so as to interfere with the processes linking stimulation and contraction.
Footnotes
- Received August 17, 1972.
- Accepted May 9, 1973.
- © 1973 by The Williams & Wilkins Co.
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