Triggered activity in atrial fibres of canine coronary sinus: role of extracellular potassium accumulation and depletion.

Abstract

1. Bursts of triggered activity can be induced in atrial fibres of the canine coronary sinus exposed to catecholamines. During a triggered burst there is an initial acceleration of rate accompanied by depolarization of the maximum diastolic potential (m.d.p.) followed by slowing of the rate and termination accompanied by hyperpolarization. 2. We have used extracellular K+-sensitive micro-electrodes (potassium ISE) to monitor extracellular K+ concentration ([K+]o) during and following triggered activity, while simultaneously measuring membrane potential with conventional intracellular micro-electrodes. 3. We found that the initial increase in rate during triggered activity is accompanied by increased [K+]o and depolarization. Later rate slowing and m.d.p. hyperpolarization is accompanied by decline of extracellular K+ accumulation. Following termination of triggered activity, extracellular K+ depletion occurred. 4. The decline of [K+]o and slowing of rate are known responses to enhanced Na+-K+ pump activation, as is the post-triggering depletion of extracellular K+. 5. Strophanthidin, which blocks the Na+-K+ pump, also blocks the [K+]o decline, the slowing of rate seen towards the end of the triggered episode, and the post-triggering depletion of extracellular K+. 6. Separate experiments studying the effects of elevated bath K+ and depolarizing current on triggering rate and delayed after-depolarization amplitude support our hypothesis that the rate profile of the triggered episode is to a large extent controlled by variations in m.d.p. subsequent to extracellular K+ accumulation and Na+-K+ pump activation.

The effect of heart rate on the arrhythmogenic transient inward current in isolated sheep cardiac Purkinje fibres.

“…6B that under these conditions only an increase in ITI would have been seen and if there was a small, slow decrease in IT, it would have gone undetected. In contrast to the reports above Henning et al (1987) observed an apparent rate-dependent decrease in the afterdepolarization in the canine coronary sinus: the after-depolarization was reduced after a burst of triggered activity. It may be important that in their study afterdepolarizations were induced by catecholamines rather than by Na'-pump block, and the bursts were typically about 250 s in duration.…”

“…Similarly, Vassalle & Mugelli (1981) have shown that IT, is enhanced in the wake of a short train of voltage-clamp pulses. Different results were obtained by Henning, Kline, Siegal & Wit (1987) who studied after-…”

“…It is therefore possible that during rapid stimulation, because of the decrease in the Ca2+ content of the sarcoplasmic reticulum, the state of Ca2+ overload lessens, and consequently active force increases. Henning et al (1987) suggested that the decrease in the after-depolarization during a burst of triggered activity in the coronary sinus may be the result of the activation of the Na+ pump during the burst of action potentials; the Na+ pump may be activated by the initial rise in extracellular K+. Although extracellular K+ was not measured in the present experiments it probably increased with the onset of rapid stimulation and this would tend to activate the Na+ pump.…”

Mechanisms underlying the modulation of arrhythmogenic events by components of ischemia in guinea pig cardiac myocytes

“…Thus, high [K], has been shown either to decrease I,, (Vassalle and Mugelli 1981) or not to modify it (Kass et al 19'78b). Similarly, in the presence of catecholamines, high [K], either decreases V, , (Coetzee and Opie 1988) or facilitates (Henning et al 1987) repetitive discharge due to Vo,.…”