The sulphonylurea glibenclamide inhibits voltage dependent potassium currents in human atrial and ventricular myocytes

1. It was the aim of our study to investigate the effects of the sulphonylurea glibenclamide on voltage dependent potassium currents in human atrial myocytes. 2. The drug blocked a fraction of the quasi steady state current (ramp response) which was activated positive to −20 mV, was sensitive to 4-aminopyridine (500 μM) and was different from the ATP dependent potassium current I(K(ATP)). 3. Glibenclamide dose dependently inhibited both, the peak as well as the late current elicited by step depolarization positive to −20 mV. The IC(50) for reduction in charge area of total outward current was 76 μM. 4. The double-exponential inactivation time-course of the total outward current was accelerated in the presence of glibenclamide with a τ(fast) of 12.7±1.5 ms and a τ(slow) of 213±25 ms in control and 5.8±1.9 ms (P<0.001) and 101±20 ms (P<0.05) under glibenclamide (100 μM). 5. Our data suggest, that both repolarizing currents in human atrial myocytes, the transient outward current (I(to1)) and the ultrarapid delayed rectifier current (I(Kur)) were inhibited by glibenclamide. 6. In human ventricular myocytes glibenclamide inhibited I(to1) without affecting the late current. 7. Our data suggest that glibenclamide inhibits human voltage dependent cardiac potassium currents at concentrations above 10 μM

NADH supplementation decreases pinacidil-primed I(K(ATP)) in ventricular cardiomyocytes by increasing intracellular ATP

1. The aim of this study was to investigate the effect of nicotinamide-adenine dinucleotide (NADH) supplementation on the metabolic condition of isolated guinea-pig ventricular cardiomyocytes. The pinacidil-primed ATP-dependent potassium current I(K(ATP)) was used as an indicator of subsarcolemmal ATP concentration and intracellular adenine nucleotide contents were measured. 2. Membrane currents were studied using the patch-clamp technique in the whole-cell recording mode at 36–37°C. Adenine nucleotides were determined by HPLC. 3. Under physiological conditions (4.3 mM ATP in the pipette solution, ATP(i)) I(K(ATP)) did not contribute to basal electrical activity. 4. The ATP-dependent potassium (K((ATP))) channel opener pinacidil activated I(K(ATP)) dependent on [ATP](i) showing a significantly more pronounced activation at lower (1 mM) [ATP](i). 5. Supplementation of cardiomyocytes with 300 μg ml(−1) NADH (4–6 h) resulted in a significantly reduced I(K(ATP)) activation by pinacidil compared to control cells. The current density was 13.8±3.78 (n=6) versus 28.9±3.38 pA pF(−1) (n=19; P<0.05). 6. Equimolar amounts of the related compounds nicotinamide and NAD(+) did not achieve a similar effect like NADH. 7. Measurement of adenine nucleotides by HPLC revealed a significant increase in intracellular ATP (NADH supplementation: 45.6±1.88 nmol mg(−1) protein versus control: 35.4±2.57 nmol mg(−1) protein, P<0.000005). 8. These data show that supplementation of guinea-pig ventricular cardiomyocytes with NADH results in a decreased activation of I(K(ATP)) by pinacidil compared to control myocytes, indicating a higher subsarcolemmal ATP concentration. 9. Analysis of intracellular adenine nucleotides by HPLC confirmed the significant increase in ATP

The pacemaker current I(f) in single human atrial myocytes and the effect of β-adrenoceptor and A(1)-adenosine receptor stimulation

1. We used single human atrial myocytes to study I(f) occurrence, properties and pharmacological modulation. Cells were obtained by chunk enzymatic digestion from samples of right atrial appendages of patients undergoing corrective cardiac surgery. 2. Patch-clamped cells in the whole-cell configuration were superfused with a modified Tyrode solution to reduce contamination by interfering currents and to amplify I(f). The average cell membrane capacitance was 85.06±2.41 pF (n=531). Data were consistent with the geometrical dimensions of the cells (length 94.2±1.89 μm, width 17.9±0.42 μm, n=126). 3. When hyperpolarizing to −120 mV from a holding potential of −40 mV, 252 of 306 tested cells (82%) expressed a hyperpolarization-activated inward current (I(f) density =3.77±0.25 pA pF(−1)); the current was considered to be present in a given cell if its density at −120 mV was larger than 0.5 pA pF(−1). 4. Current activation was sigmoidal and fitted a Boltzmann model; the average activation curve (n=25) showed a maximum current amplitude of 205.97±19.94 pA, corresponding to 3.87±0.63 pA pF(−1), voltage of half-maximal activation (V(1/2)) at −86.68±2.19 mV and a slope of −11.39±0.69 mV. The reversal potential of I(f) measured by tail-current analysis was −13.07±1.92 mV (n=6). The addition of CsCl (5 mM) fully and reversibly blocked the current. 5. In the presence of the β-adrenoceptor agonist isoprenaline (Iso, 1 μM), V(1/2) was significantly shifted toward less negative potentials by 6.06±1.96 mV (n=16, P=0.0039). The selective A(1)-adenosine receptor agonist cyclopentyladenosine (CPA, 1 μM) caused a statistically significant shift of V(1/2) toward more negative potentials with respect to the control curve, both in the absence (−7.37±1.83 mV, P=0.0005, n=11) and in the presence of 1 μM Iso (−4.97±1.78, P=0.031, n=6). 6. These results demonstrate that a current with the properties of I(f) described in cardiac primary and secondary pacemakers occurs in the majority of human atrial cells. While the pathophysiological relevance of I(f) in human atrial tissue remains to be defined, our data clearly show that it is modulated through stimulation of β-adrenoceptors and A(1)-adenosine receptors