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Role of the 293b-sensitive, slowly activating delayed rectifier potassium current, i(Ks), in pacemaker activity of rabbit isolated sino-atrial node cells.

Lei, M, Cooper, PJ, Camelliti, P and Kohl, P (2002) Role of the 293b-sensitive, slowly activating delayed rectifier potassium current, i(Ks), in pacemaker activity of rabbit isolated sino-atrial node cells. Cardiovasc Res, 53 (1). pp. 68-79.

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OBJECTIVES: (i) to characterize the electrophysiological properties of the slowly activating delayed rectifier potassium current, i(Ks), defined as the 293b-sensitive current, during the action potential (AP) of rabbit sino-atrial node (SAN) pacemaker cells; (ii) to evaluate the contribution of i(Ks) to the pacemaker AP under physiological conditions and during beta-adrenergic stimulation. METHODS: Rabbit SAN pacemaker cells were studied using the perforated patch clamp technique in voltage-, AP- and current-clamp modes. RESULTS: Voltage-clamp findings. Block of i(Ks) by 293b is dose-dependent, with an IC(50) (half block) in rabbit SAN cells of 1.35 microM and an IC(80) (sub-maximal block) of 5 microM. Sub-maximal concentrations of 293b have no significant effects on long-lasting and transient inward calcium currents, i(Ca,L) and i(Ca,T), inward hyperpolarization activated current, i(f), and transient outward current, i(to). AP-clamp experiments. The 293b-sensitive current activates near the peak of the SAN pacemaker action potential, reaches a mean maximal current density of 1.0+/-0.3 pA/pF (n=8, cell capacitances 27 to 62 pF, mean 35+/-4.0 pF) during late repolarization, and inactivates towards the end of repolarization. Additionally, in two smaller cells (cell capacitances 15 and 23 pF), no discernible 293b-sensitive current component was detected. Current-clamp data. In spontaneously beating SAN cells under control conditions, sub-maximal block of i(Ks) by 5 microM 293b has negligible effects on action potential characteristics and does not change average cycle length (n=11). In contrast, after pre-treatment with 10 nM isoprenaline to mimic beta-adrenergic stimulation, cells showed a 293b-induced depolarization of maximum diastolic potential by 2.2+/-1%, a decrease in diastolic depolarization rate by 9.9+/-4%, and a slowing of late action potential repolarization by 28.7+/-10.2%, resulting in a prolongation of spontaneous cycle length by 9.8+/-3.0% (P<0.05, n=10; for all parameters). CONCLUSION: Our findings suggest that in rabbit SAN: (i) i(Ks) is activated during the normal pacemaker AP; (ii) the contribution of i(Ks) to beating rate is small under control conditions; and (iii) i(Ks) contributes significantly to spontaneous pacemaker rate during beta-adrenergic stimulation.

Item Type: Article
Divisions : Surrey research (other units)
Authors :
Lei, M
Cooper, PJ
Kohl, P
Date : January 2002
Uncontrolled Keywords : Action Potentials, Adrenergic beta-Agonists, Animals, Chromans, Dose-Response Relationship, Drug, Isoproterenol, Patch-Clamp Techniques, Potassium Channel Blockers, Potassium Channels, Inwardly Rectifying, Rabbits, Sinoatrial Node, Sulfonamides
Related URLs :
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 10:00
Last Modified : 24 Jan 2020 18:15

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