A time-dependent and voltage-sensitive K+ current in single cells from frog atrium.

Abstract

A quantitative description of the time-dependent and voltagesensitive outward currents in heart has been hampered by the complications inherent to the multicellular preparations previously used . We have used the whole-cell patch-clamp technique to record the delayed outward K+ current, IK, in single cells dissociated from frog atrium . Na' currents were blocked with tetrodotoxin and Ca 21 currents with Mn 21 or Cd2+ . After depolarizations from -50 mV to potentials positive to -30 mV, a time-dependent outward current was observed . This current has been characterized according to its steady state activation, kinetics, and ion transfer function . The current is well described as a single Hodgkin-Huxley conductance. The deactivation of the current is a single exponential. Activation of the current is sigmoid and is fitted well by raising the activation variable to the second power. The reversal potential of IK is near EK and shifts by 57 mV/10-fold change in [K +]o. This suggests that the current is carried selectively by K ions. The threshold for activation is near -30 mV . IK is maximally activated positive to +20 mV and shows no inactivation . The fully activated current-voltage relationship is linear between -110 and +50 mV . Neither Ba t+ (250,,M) nor Cd21 (100 uM) affects IK.

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

“…The hearts were perfused with 1 mg/ml collagenase and 0'5 mg/ml trypsin for 1j h. The atria were removed and dissociated mechanically in the presence of 1-4 mg/ml collagenase and 0-6 mg/ml trypsin. It should be noted that this procedure differs significantly from that published by Simmons et al (1986). Electrophysiology IK was measured using the whole-cell configuration of the patch clamp technique (Hamill, Marty, Neher, Sakman & Sigworth, 1981).…”

“…Furthermore, Osterrieder et al (1982), Brum et al (1983), and Kameyama et al (1985Kameyama et al ( , 1986 report that internal perfusion of cells with cyclic AMP increases 'K, although detailed analyses were not published. There are some suggestions that IK may be regulated by protein kinase C as well as protein kinase A (Tohse, Kameyama & Irisawa, 1987; Simmons, Creazzo & Hartzell (1986) were used with modifications as described below.…”

A slowly activating voltage‐dependent K+ current in rat pituitary nerve terminals.

“…IKS shows marked run-down in the presence of 1 mm free Mg2+, whereas at 0 3 mm no run-down was observed (Simmons et al 1986). The current is markedly increased by isoprenaline or forskolin treatment or by internal perfusion with cAMP.…”

“…Comparison with other slow K+ currents Delayed rectifier potassium currents with extremely slow activation kinetics were originally described in Purkinje fibres (Noble & Tsien, 1969a) and were characterized in bullfrog atrial myocytes (Simmons, Creazzo & Hartzell, 1986). In guinea-pig ventricular myocytes (Matsuura, Ehara & Imoto, 1987) the current is composed of two different components, the rapidly activating 'Kr and the slowly activating IKS (Sanguinetti & Jurkiewicz, 1990).…”

“…The activation kinetics of IKS in bullfrog atrial myocytes was fitted assuming a Hodgkin-Huxley model with n = 2 and a time constant of -2 s at +5 mV (Simmons et al 1986). …”