In Vitro Responses of Nictitating Membrane to Drugs and to Denervation

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Abstract
The smooth musculature of the cat''s nictitating membrane was studied in vitro. The inferior smooth muscle was removed, divested of its connective tissue covering, and mounted in a controlled temperature muscle bath composed of oxygenated ringer buffered with phosphate and containing glucose. Isotonic contractions were recorded on a kymograph using a frontal writing lever. The responsiveness of the muscle to adrenergic and cholinergic drugs was qualitatively in agreement with the results reported in in vivo studies. The cholinesterase inhibitor DFP enhances responsiveness to acetylcholine (ACh) without otherwise affecting membrane length. ACh responsiveness is counteracted by small amounts of atropine. Denervated membranes exhibited a lowered threshold for epinephrine and norepinephrine (the sensitization being greater for the latter) and a lack of response to ephedrine. A method for recording isometric contractions by a mechano-electronic transducer has been developed for use in the conductance studies that are to follow. It is believed that, in addition to its use in study of permeability, this preparation will be of value in further elucidating the mechanism of action of various agents acting at autonomic neuro-effector junctions.

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