Relaxation of the ACh-induced potassium current in the rabbit sinoatrial node cell.
Voltage clamp experiments were carried out in order to study the mechanism of the ACh action in the rabbit S-A node cell. The following results were obtained: 1. The reversal potential of the ACh-induced current behaved like a potassium electrode, confirming that the ACh-operated channels pass potassium ions selectively. 2. On depolarizing voltage jumps the ACh-induced current showed an instantaneous peak from which the current decayed to a new steady level (relaxation). On hyperpolarizing voltage jumps the initial step change in current was followed by a gradual increase. 3. The time course of the current change on voltage jumps was well fitted by a single exponential and the time constant became longer as the membrane potential was increased. 4. The instantaneous I-V curve was linear while in the steady state the curve became flatter at low negative membrane potentials and steeper at high negative membrane potentials. The results suggest that ACh opens a specific potassium channel when the drug is bound to the muscarinic receptor. The opening and closing rate constants for this potassium channel depend on the membrane potential in such a way that on depolarizing voltage jumps the fraction of open channels gradually decreases and on hyperpolarization the fraction increases.
D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects*; D007478:Iontophoresis; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
D007473:Ion Channels; D000109:Acetylcholine; D011188:Potassium