Physiological and ultrastructural studies on the mechanism of stretch-induced contractile activation in rabbit cerebral artery smooth muscle.

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Abstract
Quick stretches applied to the helical strips of rabbit cerebral artery produced marked delayed tension development. The stretch-induced contraction was more resistant to the removal of [Ca2+]o and Ca antagonists than the mechanical response to high [K+]o and electrical stimulation, and was absent in chemically skinned preparations, indicating that it is not an inherent property of the contractile mechanism per se. The effect of the removal of [Ca2+]o and drugs such as dantrolene and ryanodine. indicated that the intracellular origin of Ca2+ was involved in the stretch-induced contraction. To explore the above possibility, the intracellular Ca localization in rabbit cerebral artery smooth muscle was examined by the pyroantimonate method. In muscle cells fixed at rest, the pyroantimonate precipitate containing Ca was localized along the inner surface of the plasma membrane, while in muscle cells fixed during the stretch-induced contraction the precipitate was diffusely distributed in the myoplasm. These results strongly suggest that the stretch-induced mechanical response is associated with the Ca2+ release from the inner surface of the plasma membrane.

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