Mechanism of potassium efflux and action potential shortening during ischaemia in isolated mammalian cardiac muscle.

Abstract

SUMMARY1. Ischaemia was simulated in the isolated sheep cardiac Purkinje fibre and guinea-pig papillary muscle by immersing the preparations in paraffin oil. lonselective microelectrodes recorded potassium (K+) and pH (pH.) in the thin film of Tyrode solution trapped at the fibre surface while other microelectrodes recorded intracellular pH (pHi), membrane potential and action potentials (AP) (evoked by field stimulation), or membrane current (two-microelectrode voltage clamp in shortened Purkinje fibres). Twitch tension was also monitored. The paraffin oil model reproduced the salient characteristics of myocardial ischaemia, i.e. a decrease of twitch tension; a decrease of pHi and pHs; a rise in K+ (by 2-3 mM); a depolarization of diastolic membrane potential; considerable shortening of the AP (up to 30% within 4 min).2. The sulphonylurea compounds, glibenclamide (200 ,UM) and tolbutamide (1 mM), known inhibitors of the KATP channel, completely blocked the ischaemic rise of K+ and prevented AP shortening. Ischaemic tension decline was notably less pronounced in the presence of sulphonylureas.3. The ischaemic increase of slope conductance (Purkinje fibre) was prevented by 1 mM-tolbutamide and 200 ,tM-glibenclamide. 4. Sulphonylureas did not affect resting membrane potential, the AP or the current-voltage relationship under non-ischaemic conditions (this also indicates that ischaemic K+ accumulation is not fuelled by the background K+ current [iKJ] which was shown, as expected, to be Ba2' sensitive).5. In a normally perfused preparation, reducing intracellular ATP by inhibiting glycolysis with 2-deoxyglucose (DOG) produced a similar AP shortening plus a membrane hyperpolarization, both of which were inhibited by tolbutamide or glibenclamide. The AP shortening was not related uniquely to the fall of pHi observed under these conditions since experimentally reducing pHi (by reducing pH.in the absence of DOG) lengthened rather than shortened the AP.6. The possibility that the ischaemic rise in K+ might be the cause of AP shortening was excluded by the observation that, in a normally perfused Purkinje fibre, experimentally reducing pHi (by an amount similar to that seen during ischaemia) completely neutralized the AP-shortening effect of an elevated K+ (from MS 8314 R. N. A. GASSER AND R. D. VA UGHAN-JONES 4-5 to 6-5 mM). Furthermore, the sulphonylurea-sensitive AP shortening seen during DOG treatment (paragraph 5) could not have been associated with a K' rise since, in these particular experiments, the fibres were well perfused and diastolic membrane potential hyperpolarized.7. Ischaemic K+ accumulation was not affected by (i) the inhibitor of lactate transport, cc-cyano-4-hydroxycinnamic acid (4 mM), (ii) a very high concentration of bumetanide (2 mM: a known high-affinity inhibitor of Na+-K+-2Cl-co-transport), and (iii) total Cl-removal. This indicates that ischaemic K+ efflux is not linked with anion movement.8. We conclude that simulated ischaemia leads to K+ accumulation through opening of sulphonylurea-sens...

The effect of glibenclamide on frog skeletal muscle: evidence for K+ATP channel activation during fatigue.

“…475.3 498 between 3 and 6 min and a maximal effect in 10-13 min. (Gasser & Vaughan-Jones, 1990;Deutch, Klitzner, Lamp & Weiss, 1991). However, one must assume that glibenclamide does not affect the K+ delayed rectifier.…”

Metabolic changes during ischaemia and their role in contractile failure in isolated ferret hearts.

“…This in turn may implicate depletion of intracellular ATP in the failure of the action potential (McDonald & MacLeod, 1973). There is considerable evidence that action potential shortening during metabolic blockade occurs as a result of an increase in outward K+ current carried by ATP-sensitive K+ channels (Vleugels, Verecke & Carmeliet, 1980;Lederer et al 1989) and recent work suggests that the same may be true for action potential shortening during ischaemia (Wilde, Escande, Schumacher, Thuringer, Mestre, Fiolet & Janse, 1990;Gasser & Vaughan-Jones, 1990). In the present study action potential duration fell by about 50 % over 3-4 min of ischaemia in glycogen-depleted hearts (Fig.…”

Effects of metabolic inhibition and changes of intracellular pH on potassium permeability and contraction of rat uterus.

“…One possibility is that it may be linked to anion transport. In studies on cardiac muscle it has been suggested that K+ efflux in hypoxia may be coupled to lactate efflux, but this remains controversial (Kleber, 1984;Gasser & Vaughan-Jones, 1990). Does increased K+ efflux in hypoxia contribute to the depression of force?…”