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Nicotine depresses the functions of multiple cardiac potassium channels
Abstract:
Nicotine is the main constituent of tobacco smoke responsible for the elevated risk of the cardiovascular disease and sudden coronary death associated with smoking, presumably by provoking cardiac arrhythmias. The cellular mechanisms may be related to the ability of nicotine to prolong action potentials and to depolarize membrane potential. However, the underlying ionic mechanisms remained unknown. We showed here that nicotine blocked multiple types of K+ currents, including the native currents in canine ventricular myocytes and the cloned channels expressed in Xenopus oocytes: A-type K+ currents (I(to)/Kv4.3), delayed rectifier K+ currents (I(Kr)/HERG) and inward rectifier K+ currents (I(K1)/Kir2.1). Most noticeably, nicotine at a concentration as low as of 10 nM significantly suppressed I(to) and Kv4.3 by approximately 20%. The effects of nicotine were independent of nicotinic receptor simulation or catecholamine release. Our results indicate that nicotine is a non-specific blocker of K+ channels and the inhibitory effects are the consequence of direct interactions between nicotine molecules and the channel proteins. Our study provided for the first time the evidence for the direct inhibition of cardiac K+ channels by nicotine and established a novel aspect of nicotine pharmacology.
Insights
Nicotine directly blocks cardiac potassium (K+) channels, disrupting normal heart electrical activity. This finding reveals a new mechanism for how smoking increases cardiovascular disease risk.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- Cardiac Electrophysiology
Background:
- Smoking is linked to cardiovascular disease and sudden cardiac death, with nicotine presumed to cause arrhythmias.
- Cellular mechanisms involve action potential prolongation and membrane depolarization, but ionic bases were unclear.
Purpose of the Study:
- To investigate the direct ionic mechanisms by which nicotine affects cardiac ion channels.
- To identify specific potassium (K+) channel subtypes inhibited by nicotine.
Main Methods:
- Electrophysiological recordings of native K+ currents in canine ventricular myocytes.
- Functional expression and characterization of cloned K+ channels (Kv4.3, HERG, Kir2.1) in Xenopus oocytes.
- Nicotine's effects were assessed independently of receptor stimulation or catecholamine release.
Main Results:
- Nicotine non-specifically blocked multiple cardiac K+ channel types, including I(to)/Kv4.3, I(Kr)/HERG, and I(K1)/Kir2.1.
- Low nicotine concentrations (10 nM) significantly suppressed A-type K+ currents (I(to)) and Kv4.3 channels by ~20%.
- Observed effects were direct interactions with channel proteins, not mediated by nicotinic receptors or catecholamines.
Conclusions:
- Nicotine acts as a direct, non-specific blocker of cardiac potassium channels.
- This direct channel inhibition provides a novel pharmacological mechanism for nicotine's adverse cardiovascular effects.
- The study establishes a new aspect of nicotine pharmacology relevant to smoking-induced heart disease.