Effect of intraluminal pressure and tone on smooth muscle Ca2+ oscillations in cremaster muscle arterioles

Abstract

Arteriolar smooth muscle cells exhibit local variation in intracellular Ca2+ (Ca2+i) levels as shown by phenomena such as sparks, flashes and waves. The exact relationship of such events to levels of intraluminal pressure and myogenic tone, however, remains unclear. Using Fluo 4 (10 μM) loaded and cannulated rat cremaster muscle arterioles, the present studies examined variations in Ca2+i levels. Changes in fluorescence were measured using a spinning disk confocal system coupled to a microscope (x60, 1.2 N.A. objective) and high speed intensified CCD. Measurements of Ca2+i were collected at 30Hz and regions of interest defined within single cells of the vessel wall. Measurements were taken at 10, 40, 70 and 100 mmHg under baseline conditions and following treatment with nifedipine (1 μM) or adenosine (10μM). Under control conditions, increasing intraluminal pressure (10 – 70 mmHg) was associated with a greater number of cells exhibiting oscillations (26 ± 2.9 to 72 ± 3.6 % of cells in a given field) and which occurred with an increasing frequency (0.1 ± 0.02 to 0.27 ± 0.03 Hz). The increase in number of cells exhibiting oscillations and increased frequency of oscillations, with increments in pressure, persisted following either nifedipine or adenosine. In contrast to arterioles exhibiting active myogenic constriction to increases in pressure, vessels exposed to nifedipine or adenosine responded largely passively. Thus, oscillations in Ca2+i are not dependent on active myogenic constriction but are influenced by pressure‐induced distention.