Separation of current induced by potassium accumulation from acetylcholine-induced relaxation current in the rabbit S-A node
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The ACh-dependent channel activation and theiK-channel activation are different processes.
The activation curve ofiK and the time constant of decay ofiK current on return from a depolarizing clamp pulse were not affected by ACh.
In the majority of the experiments the presence of an accumulation component in the extra-current elicited by ACh could not be resolved. In a few cases the amplitude of the tail current was decreased in the presence of ACh.
In the case whereiK was reduced, the fullyactivated current-voltage relationship\((\bar i_K )\) was altered in the same way as that observed when the external K concentration was increased. In this case the difference between the control and the current recorded in the presence of ACh yielded a current component having a time constant similar to that ofiK. We concluded that the decrease in the amplitude was due to an increase in K concentration in the clefts between the cells (K accumulation), associated with ACh application. No direct effect of ACh on theiK channel is apparent.
Because of the difference in the time constants of the relaxation current and the current change induced by accumulation the two processes could be clearly separated from each other.
Key wordsSinoatrial node Potassium accumulation Relaxation of acetylcholine-induced current
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