Effects of diltiazem and noradrenaline on extracellular potassium changes in the globally ischaemic rat heart.
OBJECTIVE
The aim was to investigate the effects of a calcium antagonist (diltiazem) and a catecholamine (noradrenaline) on extracellular potassium accumulation during global ischaemia.


METHODS
Extracellular potassium concentration ([K+]e) was measured during 30 min global ischaemia in the isolated rat heart using a valinomycin potassium sensitive electrode. Contracture development during ischaemia was measured throughout with an intraventricular balloon inserted into the left ventricle and myocardial adenine nucleotides were measured in separate series of hearts.


RESULTS
In control hearts, [K+]e showed a characteristic triphasic change during 30 min global ischaemia. This consisted of an early rising phase followed by a transient falling phase after the initial peak of [K+]e, and then a late rising phase. Diltiazem suppressed the rate of rise of [K+]e during early ischaemia, but extended the time course of the early [K+]e rise with the higher dose, abolishing the transient falling phase of [K+]e. During late ischaemia, the rise in [K+]e was attenuated by diltiazem. Noradrenaline also suppressed the early extracellular potassium accumulation, but in contrast to diltiazem, hastened the time course of the late [K+]e rise.


CONCLUSIONS
Although diltiazem suppresses the early potassium loss during ischaemia as previously described, the drug also decreases the [K+]e fall by some as yet unknown mechanism, so that the [K+]e level becomes higher than control during the falling phase.
Mitani
A
A
Division of Cardiovascular Surgery, Faculty of Medicine, Fukuoka, Japan.
Kinoshita
K
K
Fukamachi
K
K
Sakamoto
M
M
Kurisu
K
K
Fukumura
F
F
Tsuruhara
Y
Y
Nakashima
A
A
Tokunaga
K
K
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003326:Coronary Circulation / Q000502:physiology; D003331:Coronary Vessels / Q000378:metabolism*; D004110:Diltiazem / Q000494:pharmacology*; D004594:Electrophysiology; D017202:Myocardial Ischemia / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D016276:Ventricular Function
D000255:Adenosine Triphosphate; D004110:Diltiazem; D011188:Potassium; D009638:Norepinephrine