A novel K-ATP current in cultured neonatal rat atrial appendage cardiomyocytes

The functional and pharmacological properties of ATP-sensitive K+ (K-ATP) c hannels were studied in primary cultured neonatal rat atrial appendage card iomyocytes. Activation of a whole-cell inward rectifying K+ current depende d on the pipette ATP concentration and correlated with a membrane hyperpola rization close to the K+ equilibrium potential. The K-ATP current could be activated either spontaneously or by a hypotonic stretch of the membrane in duced by lowering the osmolality of the bathing solution from 290 to 260 mO sm/kg H2O or by the K+ channel openers diazoxide and cromakalim with EC50 a pproximate to 1 and 10 nmol/L, respectively. The activated atrial K-ATP cur rent 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 displaye d a conductance of 58.0+/-2.2 pS and opened in bursts of 133.8+/-20.4 ms du ration, with an open time duration of 1.40+/-0.10 ms and a close time durat ion of 0.66+/-0.04 ms for negative potentials. The channel had a half-maxim al open probability at 0.1 mmol/L ATP, was activated by 100 mu mol/L diazox ide, and was inhibited by glyburide, with an IC50 in the nanomolar range. T hus, pending further tests at low concentrations of K-ATP channel openers, the single-channel data confirm the results obtained with whole-cell record ings. The neonatal atrial appendage K-ATP channel thus shows a unique funct ional and pharmacological profile resembling the pancreatic beta-cell chann el for its high affinity for glyburide and diazoxide and for its conductanc e, but also resembling the ventricular channel subtype for its high affinit y for cromakalim, its burst duration, and its sensitivity to ATP. Reverse t ranscriptase-polymerase chain reaction experiments showed the expression of Kir6.1, Kir6.2, SUR1A, SUR1B, SUR2A, and SUR2B subunits, a finding support ing the hypothesis that the neonatal atrial K-ATP channel corresponds to a novel heteromultimeric association of K-ATP channel subunits.