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Myoplasmic Ca2+-force Relationship Studied With fura-2 During Stimulation of Rat Aortic Smooth Muscle

Myoplasmic Ca2+-force Relationship Studied With fura-2 During Stimulation of Rat Aortic Smooth Muscle

G Bruschi, M E Bruschi, G Regolisti, A Borghetti

Am J Physiol. 1988 May;254(5 Pt 2):H840-54.

PMID: 3364589

Abstract:

The intracellular Ca indicator fura-2 was used for simultaneous measurements of intracellular free Ca (Ca2+i) and force in arterial smooth muscle. Rat aortic medial rings were submitted to fluorometry in a geometrical arrangement resembling that of adherent cell layers. A rigid force-transducing system served to immobilize the tissue and record the developed force quasi-isometrically. Stimulation was performed with norepinephrine (NE), KCl depolarization (high K), and a nonfluorescent Ca ionophore (ionomycin) at varying extracellular Ca concentrations. The following facts were observed. NE, high K, and ionomycin increased tension along with fura-2-reported Ca2+i; under any circumstances tension was Ca2+i dependent and could be varied by manipulating Ca2+i. However, NE and high K determined a parallel increase in the effectiveness of Ca2+i in comparison with the simple ionophore, i.e., they increased the force-to-Ca2+i ratio. NE and high K produced half-maximal tension at fura-2 estimated Ca2+i of 0.10 and 0.13 microM, whereas ionomycin required 0.6 microM to achieve the same amount of force. It is inferred that Ca2+i is a determinant of vascular contraction, but some results suggest the existence of factors that sensitize the contractile machinery to Ca.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP32195554-A	Chloride ionophore I		32195-55-4	Price
AP58801346	Calcium ionophore I		58801-34-6	Price

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