Differential sensitivity of atrial and ventricular KATP channels to metabolic inhibition

Objective: The aim is to compare the activation of ATP-sensitive potassium channels (KATP channels) in intact and metabolically impaired atrial and ventricular myocytes. Methods: The KATP channel current is measured by whole cell and gramicidin-perforated patch clamp recordings in 164 cultured neonate rat cardiomyocytes. Results: In whole cell recordings with 84 μmol/l ADP in pipette, spontaneous activity is significantly higher in atrium than ventricle, and EC50 for the KATP channel opener diazoxide is 0.13 μmol/l (atrium) versus 3.1 μmol/l (ventricle). With an ATP-regenerating system in pipette, EC50 for diazoxide is 19.7 μmol/l (atrium) versus 54.9 μmol/l (ventricle). In gramicidin-perforated patch recordings, atrial myocytes respond significantly to 100 nmol/l of the mitochondrial protonophore CCCP, while ventricular myocytes do not. EC50 for diazoxide is 129 μmol/l (atrium) versus <2500 μmol/l (ventricle) for myocytes exposed to CCCP, and 676 versus <2500 μmol/l, respectively, without CCCP. Conclusions: (1) KATP channels are significantly more sensitive to metabolic inhibition in atrial than ventricular myocytes. (2) Sensitivity of atrium versus ventricle to the channel opener diazoxide increases from 3:1 to ≥24:1 with ADP or metabolic inhibition. If extended to intact hearts, the results would predict a higher atrial sensitivity to ischemia, and a high sensitivity of the ischemic atrium to KATP channel opener

A Novel K ATP Current in Cultured Neonatal Rat Atrial Appendage Cardiomyocytes

International audienceThe functional and pharmacological properties of ATP-sensitive K+ (KATP) 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 KATP 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 KATP current was highly sensitive to glyburide, with an IC50 of 1.22±0.15 nmol/L. Recorded in inside-out patches, the neonatal atrial KATP 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 KATP channel openers, the single-channel data confirm the results obtained with whole-cell recordings. The neonatal atrial appendage KATP channel thus shows a unique functional and pharmacological profile resembling the pancreatic β-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 KATP channel corresponds to a novel heteromultimeric association of KATP channel subunits