Single delayed rectifier channels in frog atrial cells. Effects of beta-adrenergic stimulation.

The patch-clamp technique with two pipettes was used to record single delayed K+ channels (cell-attached electrode) and to control the potential and the composition of the intracellular compartment (whole-cell electrode). With 30 microM cAMP in the cell and physiological potassium concentrations inside and outside the patch, a channel carrying an outward current was characterized. Its open probability was very low and the channel was recorded in only 5% of patches under control conditions. Increasing intracellular cAMP increased the probability of finding a channel in a patch 10-fold. The channel had the characteristics expected of a delayed rectifier channel. The time-course of its ensemble average resembled the whole-cell current in the same cell. The current-voltage relationship exhibited inward rectification, with a slope conductance of 20 pS in the linear portion and a reversal potential close to EK. Both the open- and the closed-time distributions were described by the sum of two exponentials, suggesting a complicated gating scheme involving two closed states and two open states. The beta-adrenergic stimulation did not change the conductance of the channel, but increased its probability of opening

Modulation of the delayed rectifier potassium current in frog cardiomyocytes by beta-adrenergic agonists and magnesium.

International audienceThe regulation of IK and ICa were studied in single cells isolated from bull-frog atrium using the whole-cell configuration of the patch clamp and a perfused patch pipette. 2. IK was increased approximately 50-100% and ICa was increased approximately 6-10 times by 1 microM-isoprenaline, 5 microM-forskolin, or internal perfusion with 30 microM-cyclic AMP. The effects of cyclic AMP and isoprenaline were not additive. The shape of the concentration-response curves and the EC50 values for the effects of cyclic AMP on ICa and on IK were very similar (2.3 microM for IK and 1.7 microM for ICa). 3. Elevation of intracellular cyclic AMP had a similar effect on IK regardless of whether ICa was blocked with Cd2+ or not. Increasing ICa with dihydropyridine Ca2+ channel agonists had no effect on IK amplitude. 4. Isoprenaline or cyclic AMP caused an increase in the fully-activated IK and also shifted the activation curves to more negative potentials in most cells. The shift in the activation curve was reversible and was also observed when ICa was blocked with Cd2+. The rate of activation of IK was increased and the rate of deactivation of IK was slowed by isoprenaline. 5. After breaking the membrane patch and initiating whole-cell recording, IK ran down with time in about 50% of the cells examined when the intracellular solution contained 1 mM [Mg2+]. In contrast, when the solution contained 0.3 mM [Mg2+], rundown was almost never observed. Internal perfusion with increasing concentrations of [Mg2+] caused reversible decreases in the maximum amplitude of IK and shifted the IK activation curve slightly to more negative potentials, but had negligible effects upon the shape or the curvature of the fully activated current-voltage relationship