NDLI: Rapidly and slowly activating components of delayed rectifier K+ current in guinea-pig sino-atrial node pacemaker cells

Content Provider	PubMed Central
Author	Matsuura, Hiroshi Ehara, Tsuguhisa Ding, Wei-guang Mariko, Omatsu-kanbe Isono, Takahiro
Copyright Year	2002
Abstract	The components and properties of the delayed rectifier K+ current (I K) in isolated guinea-pig sino-atrial (SA) node pacemaker cells were investigated using the whole-cell configuration of the patch-clamp technique. An envelope of tails test was conducted by applying depolarizing pulses from a holding potential of −50 mV to +30 mV for various durations ranging from 40 to 2000 ms. The ratio of the tail current amplitude elicited upon return to the holding potential to the magnitude of the time-dependent outward current activated during depolarizing steps was dependent on the pulse duration, while after exposure to the selective I Kr inhibitor E-4031 (5 μm) this current ratio became practically constant irrespective of the pulse duration. These observations are consistent with the presence of the E-4031-sensitive, rapidly activating and E-4031-resistant, slowly activating components of I K (I Kr and I Ks, respectively) in guinea-pig SA node cells. The activation range for I Kr, defined as the E-4031-sensitive current (half-maximal activation voltage (V 1/2) of −26.2 mV) was much more negative than that for I Ks, defined as the E-4031-resistant current (V 1/2 of +17.2 mV). I Kr exhibited a marked inward rectification at potentials positive to −50 mV, whereas I Ks showed only a slight rectification. In the current-clamp experiments, bath application of E-4031 (0.5 and 5 μm) initially slowed the repolarization at potentials negative to approximately −30 mV and produced a significant depolarization of the maximum diastolic potential, followed by the arrest of electrical activity, thus indicating that the late phase of the repolarization leading to the maximum diastolic potential at around −60 mV in spontaneous action potentials is primarily produced by I Kr in guinea-pig SA node cells. External application of the selective I Ks inhibitor 293B (30 μm) also delayed the repolarization process at potentials negative to about −20 mV and induced moderate depolarization of the maximum diastolic potential leading to the arrest of the spontaneous activity. These results provide evidence to suggest that both I Kr and I Ks are present and play crucial roles in the spontaneous electrical activity of guinea-pig SA node pacemaker cells.
Related Links	http://dx.doi.org/10.1113/jphysiol.2001.016741
Starting Page	815
File Format	PDF
ISSN	14697793
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 3
Volume Number	540
Language	English
Publisher	Blackwell Science Inc
Publisher Date	2002-05-01
Access Restriction	Open
Rights Holder	Blackwell Science Inc
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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