Stimulus‐specific patterns of intracellular calcium levels in smooth muscle of ferret portal vein.

Abstract

SUMMARY1. Aequorin was loaded into cells of the ferret portal vein in order to follow intracellular Ca2+ levels during smooth muscle contraction.2. In response to a single d.c. pulse, the aequorin signal reaches a peak during the rising phase of the evoked force transient and begins to rapidly fall while force is still rising.3. In response to the addition of phenylephrine to the bathing solution, the aequorin signal rises rapidly to a peak while force is still rising but then falls rapidly to a lower level from which it declines more slowly, staying above base-line levels as long as force is maintained.4. In response to the elevation of K+ concentration in the bathing solution, light and force rise together and the elevated light level is maintained as long as is force.5. With increasing concentrations of K+, force increases up to a concentration of 50-60 mm but light increases up to 90 mm, suggesting that at a concentration of 50-60 mM-K+, the Ca2+ concentration may be saturating with respect to a site of action on the contractile apparatus.6. During the period of force maintenance, phenylephrine produces a larger ratio of force to light than does K+ depolarization.7. The maintenance of force in the presence of either phenylephrine or elevated K+ requires an elevation of intracellular Ca2+ levels above base-line values.8. These results suggest that phenylephrine can increase the effectiveness of Ca2+ on the contractile apparatus.

Effects of diltiazem on calcium concentrations in the cytosol and on force of contractions in porcine coronary arterial strips

“…Loading the strips with fura-2 did not alter the time courses and the maximum levels of tension development during 118 mm Kt-depolarization, thereby suggesting that tissue damage by possible acidification of the cells due to formaldehyde released on acetoxymethyl-ester hydrolysis did not occur (Tsien et al, 1982;Rink & Pozzan, 1985 (Figure 8). This suggests that receptor-mediated stimulation increased Ca2+-sensitivity of the contractile apparatus (Morgan & Morgan, 1984;Bruschi et al, 1988;Himpens & Somlyo, 1988;Rembold & Murphy, 1988;Sato et al, 1988). In addition, the [Ca2 t]i-tension relationship of the Ca2 '-induced contraction during depolarization was similar to the pCa-tension relationship noted with skinned fibres of the porcine coronary artery and of others (Saida & Nonomura, 1978;Kuriyama et al, 1982).…”

Protein kinase C translocation in intact vascular smooth muscle strips

“…The time courses of the generation of these two messengers are different. The increase in cytosolic free Ca2+ is only transient, and the Ca2+ concentration returns to near-basal levels within several minutes [9,10]. On the other hand, it has been shown that the increase in DAG concentration is sustained [6][7][8].…”

Effects of endothelin on the mechanical activity and cytosolic calcium levels of various types of smooth muscle

“…It has been reported that noradrenaline in rat aorta Sato et al, 1988b), carbachol in bovine trachea (Takuwa et al, 1987) and phenylephrine in ferret vascular smooth muscles (Morgan & Morgan, 1984;DeFeo & Morgan, 1985) induces greater contraction than high K+ at a given [Ca2"]cyt, possibly by the increase in Ca 2-sensitivity of contractile elements. In addition, noradrenaline and prostaglandin F2, induce sustained contraction without changing [Ca2+],Y, in Ca2"-free solution .…”