To elucidate whether K+ channels are involved in the
ischemia-reperfusion injury in immature heart, we examined the effect of
cromakalim, a potent opener of
ATP-sensitive K+
channel (KATP channel), on the ischemic and reperfused neonatal New Zealand white rabbit heart. The experiments were divided into control group and
cromakalim pretreated group. When, the heart was loaded with 10 microM
cromakalim preischemically, the recovery of heart rate and left ventricular developed pressure were significantly improved than those of the control group. Pretreatment with
cromakalim also decreased
lactate excretion in the coronary effluent. Measurements of
cation contents with atomic absorption method revealed that intracellular K+ content was lower in
cromakalim pretreated group at preischemia, end of
ischemia and 20 min after
ischemia. Intracellular accumulation of Na+ and Ca2+ at reperfusion period was inhibited by
cromakalim pretreatment. From these results, it is assumed that
cromakalim might act on
KATP channels of plasma membrane and reduces the K+ content of the cardiomyocytes which in turn inhibits Na+ and Ca2+ accumulation during the reperfusion period. Prevention of Na+ and Ca2+ accumulation after
ischemia might be a reason for cardioprotective effect of
cromakalim on neonatal New Zealand white rabbit heart.