Binding of 125I‐physalaemin to rat parotid acinar cells.

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Abstract
The binding of [125I]physalaemin to rat parotid acinar cells was investigated. The [125I]physalaemin exhibited a small degree of specific binding that was rapid, reversible and saturable. The EC50 values for inhibition of binding by 4 peptides were well correlated with their ability to activate Ca-dependent K release from the rat parotid gland. The number of binding sites, which may represent substance P receptors, was estimated to be in the range of 200/cell, a value quite different from those reported previously for muscarinic (1840/cell) or .alpha.-adrenergic (15,000/cell) receptors. If these receptors regulate the same population of Ca channels, then the mechanism or perhaps efficiency by which this is achieved may differ for the 3 receptors.