A kinetic model for the muscarinic action of acetylcholine
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The timecourse of the membrane hyperpolarization evoked by stimulation of postganglionic parasympathetic nerve endings in isolated atria from the guineapig heart is mainly governed by two exponentials, one describing most of the rising phase (rate constant kα=2.88±1.135 s−1) and one which completely describes the decline of the response (kβ=0.58±0.31 s−1). An exact description of the muscarinic receptor mediated potential change, which also allows for its apparent latency and its s-shaped beginning, is found if two additional faster exponentials are introduced. In agreement with earlier results a model of four consecutive reactions is presented. It is concluded that during muscarinic cholinergic transmission reactions subsequent to binding of the ACh-molecules to the receptor are rate-limiting.
Key wordsAcetylcholine Muscarinic receptor Consecutive reaction model Atrial membrane potential
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