FUNCTIONS OF CYCLIC-AMP AND CALCIUM AS ALTERNATIVE SECOND MESSENGERS IN PAROTID-GLAND AND PANCREAS

Abstract

Biochemical and ultrastructural studies of rat parotid gland slices led to the identification of .alpha.- and .beta.-adrenergic receptors and a cholinergic receptor, all operating within the same secretory cell. While cyclic[c]AMP serves as the 2nd messenger in the .beta.-adrenergic response of enzyme secretion, Ca2+ serves as the 2nd messenger in the .alpha.-adrenergic and in the cholinergic responses leading to K+ release and H2O secretion. Ca2+ serves as a 2nd messenger for the muscarinic cholinergic receptor in rat pancreas slices where it causes enzyme secretion. Neither the neurotransmitter, the receptor, nor the 2nd messenger are unique for a certain type of response. The latter seems to be dictated by a component of the specific response pathway affected by the 2nd or a subsequent messenger. By having different neurotransmitters operate the same response and a single neurotransmitter operate different responses, diversity of control is achieved.