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(Circulation Research. 1999;85:707-715.)
© 1999 American Heart Association, Inc.

Cellular Biology

A Novel K_ATP Current in Cultured Neonatal Rat Atrial Appendage Cardiomyocytes

Anne Baron, Laurianne van Bever, Dominique Monnier, Angela Roatti, Alex J. Baertschi

From the Department of Physiology, Centre Médical Universitaire, Geneva, Switzerland.

Correspondence to Alex J. Baertschi, Department of Physiology, Centre Médical Universitaire, 1 rue Michel Servet, CH-1211 Geneva 4, Switzerland. E-mail Alex.Baertschi{at}medecine.unige.ch

Abstract—The functional and pharmacological properties of ATP-sensitive K⁺ (K_ATP) channels were studied in primary cultured neonatal rat atrial appendage cardiomyocytes. Activation of a whole-cell inward rectifying K⁺ current depended on the pipette ATP concentration and correlated with a membrane hyperpolarization close to the K⁺ equilibrium potential. The K_ATP current could be activated either spontaneously or by a hypotonic stretch of the membrane induced by lowering the osmolality of the bathing solution from 290 to 260 mOsm/kg H₂O or by the K⁺ channel openers diazoxide and cromakalim with EC₅₀ 1 and 10 nmol/L, respectively. The activated atrial K_ATP current was highly sensitive to glyburide, with an IC₅₀ of 1.22±0.15 nmol/L. Recorded in inside-out patches, the neonatal atrial K_ATP channel displayed a conductance of 58.0±2.2 pS and opened in bursts of 133.8±20.4 ms duration, with an open time duration of 1.40±0.10 ms and a close time duration of 0.66±0.04 ms for negative potentials. The channel had a half-maximal open probability at 0.1 mmol/L ATP, was activated by 100 µmol/L diazoxide, and was inhibited by glyburide, with an IC₅₀ in the nanomolar range. Thus, pending further tests at low concentrations of K_ATP channel openers, the single-channel data confirm the results obtained with whole-cell recordings. The neonatal atrial appendage K_ATP channel thus shows a unique functional and pharmacological profile resembling the pancreatic ß-cell channel for its high affinity for glyburide and diazoxide and for its conductance, but also resembling the ventricular channel subtype for its high affinity for cromakalim, its burst duration, and its sensitivity to ATP. Reverse transcriptase–polymerase chain reaction experiments showed the expression of Kir6.1, Kir6.2, SUR1A, SUR1B, SUR2A, and SUR2B subunits, a finding supporting the hypothesis that the neonatal atrial K_ATP channel corresponds to a novel heteromultimeric association of K_ATP channel subunits.

Key Words: K_ATP channel • sulfonylurea receptor • cardiac atrium • atrial natriuretic peptide • patch clamp

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