Role of pertussis toxin-sensitive G protein in metabolic vasodilation of coronary microcirculation

We have previously demonstrated that pertussis toxin (PTX)-sensitive G protein (GPTX) plays a major role in coronary microvascular vasomotion during hypoperfusion. We aimed to elucidate the role of GPTX during increasing metabolic demand. In 18 mongrel dogs, coronary arteriolar diameters were measured by fluorescence microangiography using a floating objective. Myocardial oxygen consumption (MV˙o 2) was increased by rapid left atrial pacing. In six dogs, PTX (300 ng/ml) was superfused onto the heart surface for 2 h to locally block GPTX. In eight dogs, the vehicle (Krebs solution) was superfused in the same way. Before and after each treatment, the diameters were measured during control (130 beats/min) and rapid pacing (260 beats/min) in each group. Metabolic stimulation before and after the vehicle treatment caused 8.6 ± 1.8 and 16.1 ± 3.6% dilation of coronary arterioles <100 μm in diameter (57 ± 8 μm at control, n = 10), respectively. PTX treatment clearly abolished the dilation of arterioles (12.8 ± 2...