Influence of oxygenation on endothelial modulation of coronary vasomotor function during hyperkalemic cardioplegia.
BACKGROUND
The purpose of this study was to determine the influence of oxygenation of a hyperkalemic cardioplegic solution (K-CP) on endothelial modulation of vasomotor tone and to correlate these changes with the intracellular calcium concentration ([Ca++]i) in microvascular smooth muscle.


METHODS
Rat coronary arterioles were studied in a pressurized, no-flow normothermic state. Simultaneous monitoring of luminal diameter and [Ca++]i (fura-2) was performed with use of microscopic image analysis. Vessels were subjected to 60 minutes of oxygenated or hypoxic K-CP (K+ = 25.0 mmol/L) and were then reperfused with oxygenated Krebs-physiologic saline solution for 60 minutes.


RESULTS
In oxygenated K-CP, the K-CP-induced contraction and [Ca++]i accumulation were significantly increased in endothelium-denuded (ED) vessels compared with endothelium-intact vessels. The effect of ED in oxygenated K-CP was mimicked by administration of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine. Conversely, in hypoxic K-CP the contraction was significantly attenuated in ED vessels compared with endothelium-intact vessels, although there was no significant difference in [Ca++]i. Indomethacin did not affect the endothelium-dependent contraction during hypoxic K-CP.


CONCLUSIONS
Endothelium-derived nitric oxide modulates the vascular tone during K-CP by regulating the vascular smooth muscle [Ca++]i, whereas endothelium-derived contracting factor(s), which is not predominantly a product of cyclo-oxygenase, may play a prominent role under hypoxic K-CP by increasing vascular smooth muscle Ca++ sensitivity.
Matsuda
N
N
Department of Surgery, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
Tofukuji
M
M
Morgan
K G
KG
Sellke
F W
FW
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002314:Cardioplegic Solutions / Q000494:pharmacology*; D003331:Coronary Vessels / Q000502:physiology*; D004730:Endothelium, Vascular / Q000502:physiology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology; D010100:Oxygen / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014661:Vasoconstriction / Q000187:drug effects*
D002314:Cardioplegic Solutions; D009569:Nitric Oxide; D011188:Potassium; D010100:Oxygen; D002118:Calcium