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1. Single atrial myocytes were enzymatically isolated from the bull-frog as previously described (Hume & Giles, 1981), and patch-clamp techniques were used in an attempt to identify and separate two inwardly rectifying K+ channels in this tissue. 2. Single-channel measurements consistently demonstrated the existence of two different resting K+ channels, which both exhibited strong inward rectification. The unitary conductances of these K+ channels were 34 +/- 4 and 22 +/- 3 pS (mean +/- S.D., at 22-24 degrees C) when measured with 110 mM-K+ in the pipette solution, and their mean open times were 0.87 +/- 0.33 and 129.9 +/- 49.4 ms, respectively. 3. In the absence of acetylcholine (ACh) in the pipette, openings of the larger channels with the shorter open times occurred at a very low frequency. When ACh was present in the patch pipette, the activity of this channel increased significantly, although the single-channel conductance and gating behaviour were very similar either with or without ACh in the pipette. 4. The zero-current voltage (extrapolated from the inward currents through these types of channels) depended on the extracellular K+ concentration. [K+]o, in the fashion expected for a predominantly K(+)-selective channel: it shifted by 58 mV for a tenfold change in [K+]o. Very similar results were obtained from whole-cell voltage-clamp measurements (53 mV for a tenfold change in [K+]o). 5. The conductance of both types of K+ channels depended on [K+]o. The single-channel conductances were 25 +/- 3 and 13 +/- 2 pS with 50 mM [K+]o, and 19 +/- 4 and 9 +/- 2 pS with 20 mM [K+]o, respectively. 6. These results demonstrate that two types of resting inwardly rectifying K+ channels can be identified in single atrial myocytes. One of these is an inwardly rectifying K+ channel (IK1) previously identified in whole-cell voltage-clamp experiments (Hume & Giles, 1983). The second channel is the muscarinic receptor-regulated K+ channel (IK(ACh) which was first described in mammalian nodal and atrial cells. 7. N-Ethylmaleimide (NEM), a reagent which alkylates sulphydryl groups, affects these two types of K+ channels differentially. In the cell-attached patch configuration, bath application of NEM (50 microM) completely abolished the activity of IK(ACh), without affecting the IK1 channel activity. 8. To obtain further evidence that these two currents, IK1 and IK(ACh), were different, the inside-out patch-clamp technique was used.(ABSTRACT TRUNCATED AT 400 WORDS)
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
January 1988,
Molecular and cellular biochemistry,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
December 1999,
The Journal of biological chemistry,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
April 2001,
The Journal of physiology,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
July 1999,
Nature cell biology,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
November 2000,
American journal of physiology. Gastrointestinal and liver physiology,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
September 1993,
Trends in pharmacological sciences,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
October 2007,
Pflugers Archiv : European journal of physiology,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
October 1999,
News in physiological sciences : an international journal of physiology produced jointly by the International Union of Physiological Sciences and the American Physiological Society,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
January 1990,
The Japanese journal of physiology,
R B Clark, and
T Nakajima, and
W Giles, and
K Kanai, and
Y Momose, and
G Szabo
April 1998,
The Journal of surgical research,
