Propagated endothelial Ca2+ waves and arteriolar dilation in vivo: measurements

Abstract—To study endothelial cell (EC) – specific Ca2 signaling in vivo we engineered transgenic mice in which the Ca2 sensor GCaMP2 is placed under control of endogenous connexin40 (Cx40) transcription regulatory elements within a bacterial artificial chromosome (BAC), resulting in high sensor expression in arterial ECs, atrial myocytes, and cardiac Purkinje fibers. High signal/noise Ca2 signals were obtained in Cx40BAC-GCaMP2 mice within the ventricular Purkinje cell network in vitro and in ECs of cremaster muscle arterioles in vivo. Microiontophoresis of acetylcholine (ACh) onto arterioles triggered a transient increase in EC Ca2 fluorescence that propagated along the arteriole with an initial velocity of 116 m/s (n28) and decayed over distances up to 974 m. The local rise in EC Ca2 was followed (delay, 83060 ms; n8) by vasodilation that conducted rapidly (mm/s), bidirectionally, and into branches for distances exceeding 1 mm. At intermediate distances (300 to 600 m), rapidly-conducted vasodilation occurred without changing EC Ca2, and additional dilation occurred after arrival of a Ca2 wave. In contrast, focal delivery of sodium nitroprusside evoked similar local dilations without Ca2 signaling or conduction. We conclude that in vivo responses to ACh in arterioles consists of 2 phases: (1) a rapidly-conducted vasodilation initiated by a local rise in EC Ca2 but independent of EC Ca2 signaling at remote sites; and (2) a slower complementary dilation associated with a Ca2 wave that propagates along the endothelium. (Circ Res. 2007;101:1300-1309.) Key Words: bacterial artificial chromosome calcium imaging microcirculation Purkinje cell