Abstract
Calcium acting through the ionophore A-23187 caused massive K+ release from rat parotid slices. The ionophore thus simulates the action of epinephrine on the α-adrenergic receptor in this system. The α-adrenergic and cholinergic receptors are, however, not involved in the action of the ionophore since phetolamine and atropine had no effect on the ionophore-induced K+ release. Amylase secretion, which is induced by epinephrine through the β-adrenergic receptor but does not require Ca++ in the medium, was only slightly increased by the ionophore in the presence of Ca++. The K+ released by Ca++ through the ionophore was regained by the cells upon chelation of Ca++ with ethylene glycol bis(β-aminoethyl ether)-N,N′-tetraacetic acid. Similar to the action of epinephrine on the α-adrenergic receptor, the K+ release induced by the ionophore is specific for Ca++, which cannot be substituted by 2.5 mM Sr++, Mg++, or Ba++. The results suggest that epinephrine, like the ionophore, introduces Ca++ into the cell to mediate K+ release. It is proposed that the ionophore A-23187 may be an effective probe to test whether other Ca++-requiring hormones and neurotransmitters act in a similar fashion to produce their diverse physiological responses.
Keywords: Ca++ requirement for hormone action, K+ release, Ca++ permeability
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Selected References
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