Article date: February 1997
By: A. S. V. BURGEN, L. SPERO, in Volume 120, Issue S1, pages 317-333
. A method is described for measuring continuously the efflux of potassium or rubidium from smooth muscle of the guinea‐pig.
. Muscarinic drugs cause at maximum a 100‐fold increase in the efflux rate, due to a direct increase in permeability and only to a minor extent secondary to depolarization. With acetylcholine the dose response curve for producing efflux is displaced to 1,000 times higher concentrations than that for contraction.
. The shift varies with different agonists. The efflux and contractile responses to agonists are antagonized to an equivalent extent by atropine and several other reversible antagonists but benzhexol has a relatively greater effect on efflux. An estimate of spare receptors was obtained with benzilylcholine mustard and was similar for both responses. Dibenamine and local anaesthetics led to a parallel shift of the contraction dose response curve but a depression without shift in the efflux response.
. The most satisfactory explanation of these results is that there are two types of the muscarinic receptor in the smooth muscle of the guinea‐pig intestine.
. A method is described for measuring continuously the efflux of potassium or rubidium from smooth muscle of the guinea‐pig.
. Muscarinic drugs cause at maximum a 100‐fold increase in the efflux rate, due to a direct increase in permeability and only to a minor extent secondary to depolarization. With acetylcholine the dose response curve for producing efflux is displaced to 1,000 times higher concentrations than that for contraction.
. The shift varies with different agonists. The efflux and contractile responses to agonists are antagonized to an equivalent extent by atropine and several other reversible antagonists but benzhexol has a relatively greater effect on efflux. An estimate of spare receptors was obtained with benzilylcholine mustard and was similar for both responses. Dibenamine and local anaesthetics led to a parallel shift of the contraction dose response curve but a depression without shift in the efflux response.
. The most satisfactory explanation of these results is that there are two types of the muscarinic receptor in the smooth muscle of the guinea‐pig intestine.
DOI: 10.1111/j.1476-5381.1997.tb06813.x
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