Calcium measurement in isolated arterioles during myogenic and agonist stimulation

Abstract

Vascular smooth muscle calcium was measured during agonist treatment or pressure-induced stimulation of the myogenic response in isolated first-order skeletal muscle arterioles. Arterioles (40-180 microns) with spontaneous tone were isolated from rat cremaster muscle and cannulated. Arterioles were loaded with the calcium-sensitive dye fura-2 and excited at 340 and 380 nm. Images of vessel fluorescence were formed with a fluorescence microscope and digitized using an image processor coupled to a low light level camera. The fluorescent images allowed individual vascular smooth muscle cells to be seen within the arteriolar wall. Fluorescent intensity of the vessel wall, expressed as the ratio of fluorescence at 340 nm/380 nm, was used to estimate changes in vessel wall calcium. Topical application of norepinephrine (10 microM) to the arterioles caused a rapid and sustained constriction of the arterioles (64% of basal diam). The calcium response was biphasic consisting of a transient spike to 271% of basal followed by a decrease to a new steady state at 143% of basal. In comparison, steady-state indolactam (1 microM) produced a similar degree of constriction without an increase in calcium. Adenosine significantly dilated (35%) the arterioles and produced a decrease (24%) in vessel wall calcium. To investigate the myogenic response, intravascular pressure was step increased from 90 to 130 cmH2O. Increasing intravascular pressure caused an initial increase in vessel diameter of approximately 5% followed by active constriction that returned diameter to basal diameter. In association with this diameter change, estimated vessel wall calcium increased rapidly 8 +/- 2% and then continued to increase more slowly and remained elevated at 10-15% above basal levels. This study demonstrates the successful application of calcium-imaging technology in isolated arterioles for study of the role of calcium in arteriolar function. Results indicate that the calcium-contraction relationship differs for different agonists and are further consistent with a role for pressure-induced increases in vascular smooth muscle calcium during the myogenic response.

Dynamic characteristics and underlying mechanisms of renal blood flow autoregulation in the conscious dog

“…The observed response time in the range of 30 s is very similar to those observed by other authors in visualized arterioles in the hindlimb muscle of cats (25) and dogs (16,18) as well as in the cremaster muscle of rats (22,36). The direct comparison in the present study of the vascular responses in the renal and the hindlimb circulation in animals of the same strain (in 3 of them, also in the same individuals) clearly shows that there is a distinct difference in the time course of the myogenic response in these two vascular beds.…”

Inhibition of the active lymph pump by flow in rat mesenteric lymphatics and thoracic duct

“…In the experiments to study the time dependencies of the effects of flow on the lymph pump, ejection fraction and fractional pump flow were normalized to the values seen at the start of these protocols (0 cmH 2 O pressure gradient conditions). Normalizations of a similar nature are commonly used in lymphatic von der Weid et al , 2001Hollywood et al 1997;Mizuno et al 1998Mizuno et al , 1999von der Weid, 1998;Koller et al 1999;Shirasawa et al 2000) and other microcirculatory studies (Kuo et al 1988Meininger et al 1991;Hill & Gould, 1997;Hiramatsu et al 1998;Guibert & Beech, 1999).…”

Regulation of arterial diameter and wall [Ca2+] in cerebral arteries of rat by membrane potential and intravascular pressure

“…Conversely, many vasoconstrictors have been shown to depolarize arterial smooth muscle. Intravascular pressure has been shown to elevate intracellular [Ca¥] in cremaster muscle arterioles (Meininger, Zawieja, Falcone, Hill & Davey, 1991;D'angelo, Davis & Meininger, 1997). However, the underlying mechanism or precise relationships amongst membrane potential, arterial wall [Ca¥] and blood vessel diameter have not been completely defined in cerebral or other small arteries.…”