Atropine resistance and muscarinic receptors in the rat urinary bladder.
The action of an anticholinesterase and an antimuscarinic drug upon nerve-induced contractions of the rat urinary bladder were examined during transmural stimulation at 20 Hz. Responses were graded in magnitude by limiting the duration of the stimulus trains. 2 Responses of low magnitude produced by short stimulus trains were unchanged by atropine; however, maximal responses resulting from long stimulus trains were diminished in magnitude and shortened in duration. 3 Responses of small magnitude elicited by short stimulus trains involve muscarinic receptors in close proximity to the neuroeffector junction and are resistant to atropine. 4 Maximal responses elicited by long stimulus trains involve 'junctional' muscarinic receptors as well as receptors located at the periphery of the junction; the 'extrajunctional' receptors are blocked by atropine. 5 Responses of low magnitude produced by short stimulus trains were unaffected by echothiophate; however, the duration of maximal responses resulting from the long stimulus trains was extended. 6 The inhibition of cholinesterase did not increase the occupation of muscarinic receptors by the transmitter; however, after large quantities of transmitter were released by the long stimulus trains the association between the receptors and acetylcholine was prolonged.
D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D004456:Echothiophate Iodide / Q000494:pharmacology; D004558:Electric Stimulation; D009119:Muscle Contraction / Q000187:drug effects*; D010525:Peripheral Nerves / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011950:Receptors, Cholinergic / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D001285:Atropine; D004456:Echothiophate Iodide