KATP channel activation induces ischemic preconditioning of the endothelium in humans in vivo

BACKGROUND

Endothelial dysfunction contributes to ischemia-reperfusion injury (IRI) and is reduced by ischemic preconditioning (IPC). IPC may involve activation of ATP-sensitive potassium channels (K(ATP)). We determined whether modulation of K(ATP) channels occurs in endothelial IPC in humans.

METHODS AND RESULTS

IRI of the forearm was induced by inflating a blood pressure cuff to 200 mm Hg for 20 minutes in healthy volunteers. K(ATP) activation was modulated by intra-arterial glibenclamide (blocker) and diazoxide (opener). Endothelial function (response to intra-arterial acetylcholine) was assessed with forearm plethysmography before and after (1) 15-minute reperfusion, (2) IRI preceded by IPC (3 five-minute periods of ischemia), (3) IRI preceded by IPC with glibenclamide, (4) IPC followed by glibenclamide before IRI, (5) IRI preceded by diazoxide, and (6) IRI preceded by coinfusion of glibenclamide with diazoxide. IRI caused endothelial dysfunction (P=0.002), which IPC prevented (P=0.40). Glibenclamide abolished IPC when given contemporaneously with (P=0.003) or during IRI (P=0.0005). Diazoxide prevented endothelial dysfunction after IRI (P=0.68) but not when coinfused with glibenclamide.

CONCLUSIONS

Glibenclamide abolishes and diazoxide mimics endothelial IPC in humans. The time course of the effect of glibenclamide suggests involvement of K(ATP) channels as effectors of endothelial IPC in vivo. These data may have implications for understanding the therapeutic role of agents that modulate K(ATP) channel function.

Influence of muscle temperature during fatiguing work with the first dorsal interosseous muscle in man: a 31P-NMR spectroscopy study

Six healthy subjects rapidly lifted and lowered a small (250 g) weight with the first dorsal interosseous muscle (FDI) of one hand while the work performed was recorded continuously until fatigue (defined as losing the ability to continue lifting). Work was recorded in units of chart recorder trace displacement from baseline (centimeters) as an isotonic transducer followed the movement of the weight. In all experiments, the temperature of the hand was first adjusted by immersion in a controlled-temperature water bath. In the warmest condition, the skin surface temperature over the FDI was 30.5(0.30) degrees C [mean (SE)]. After moderate cooling, this surface temperature was 21.5(0.16) degrees C. Cooling significantly reduced the time taken to reach fatigue and more than halved the work capacity. An intermediate degree of cooling was also used in four subjects, showing that most of the effects seen were changing incrementally. Before work, and at fatigue, intracellular metabolic conditions in the FDI were studied by phosphorus nuclear magnetic resonance (31P-NMR) spectroscopy, with occlusion of the blood flow maintained during measurements. The mean intracellular pH of the FDI was also calculated. The changes observed were all consistent with the fact that intense work requires energy which must be derived largely from intracellular stores of phosphocreatine and glycogen. Less work made less demand upon reserves, and created lower concentrations of waste products and by-products. The observations did not, however, allow us to explain why fatigue occurred at a particular point or why work capacity was reduced by cooling.