ISSN:
1432-1424
Keywords:
Key words: Patch-clamp technique — Human ventricular myocytes — G proteins — Muscarinic K+ channel — Inwardly-rectifying K+ channel
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract. Muscarinic receptor-linked G protein, G i , can directely activate the specific K+ channel (I K(ACh)) in the atrium and in pacemaker tissues in the heart. Coupling of G i to the K+ channel in the ventricle has not been well defined. G protein regulation of K+ channels in isolated human ventricular myocytes was examined using the patch-clamp technique. Bath application of 1 μm acetylcholine (ACh) reversibly shortened the action potential duration to 74.4 ± 12.1% of control (at 90% repolarization, mean ±sd, n= 8) and increased the whole-cell membrane current conductance without prior β-adrenergic stimulation in human ventricular myocytes. The ACh effect was reversed by atropine (1 μm). In excised inside-out patch configurations, application of GTPγS (100 μm) to the bath solution (internal surface) caused activation of I K(ACh) and/or the background inwardly-rectifying K+ channel (I K1) in ventricular cell membranes. I K(ACh) exhibited rapid gating behavior with a slope conductance of 44 ± 2 pS (n= 25) and a mean open lifetime of 1.8 ± 0.3 msec (n= 21). Single channel activity of GTPγS-activated I K1 demonstrated long-lasting bursts with a slope conductance of 30 ± 2 pS (n= 16) and a mean open lifetime of 36.4 ± 4.1 msec (n= 12). Unlike I K(ACh), G protein-activated I K1 did not require GTP to maintain channel activity, suggesting that these two channels may be controlled by G proteins with different underlying mechanisms. The concentration of GTP at half-maximal channel activation was 0.22 μm in I K(ACh) and 1.2 μm in I K1. Myocytes pretreated with pertussis toxin (PTX) prevented GTP from activating these channels, indicating that muscarinic receptor-linked PTX-sensitive G protein, G i , is essential for activation of both channels. G protein-activated channel characteristics from patients with terminal heart failure did not differ from those without heart failure or guinea pig. These results suggest that ACh can shorten the action potential by activating I K(ACh) and I K1 via muscarinic receptor-linked G i proteins in human ventricular myocytes.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002329900217
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