Intravascular pressure-evoked changes in intracellular calcium [Ca²⁺]_i and tone in rat mesenteric and rabbit cerebral arteries in vitro

Abstract

The degree of myogenic response varies between different vascular beds and may contribute to differences in autoregulation. This study examined whether differences in pressure-induced changes in intracellular calcium ([Ca²⁺]_i) account for this variability by comparing responses in rabbit cerebral arteries which possess a prominent myogenic response with rat mesenteric arteries where the response is much less marked. Rat mesenteric small arteries and small branches of the posterior cerebral artery were mounted on glass pipettes in a perfusion myograph containing physiological saline at 37°C and aerated with 95% O₂ and 5% CO₂ under pressure and no flow conditions. Outer diameters of arteries were measured using a video dimension analyser. Vessel diameters were measured following exposure to 30, 60 and 90 mm Hg intralumenal distending pressure in the presence and absence of extracellular Ca²⁺ to determine the degree of active tone. In subsequent studies vessels were loaded with fura-2AM to allow measurement of changes in [Ca²⁺]_i in response to the same conditions. Significant active tone was only seen at 60 mm Hg in rat mesenteric small arteries. In contrast, posterior cerebral arteries possessed active tone at all distending pressures. Increases in pressure were associated with rises in [Ca²⁺]_i to similar extents in both vessel types. These data suggest that changes in [Ca²⁺]_i in response to pressure changes in rabbit cerebral and rat mesenteric small arteries are similar despite differences in myogenic tone. The contrasting behaviour of these vessels may therefore reflect other factors such as differences sensitivity of the contractile machinery to [Ca²⁺]_i.