Role of calcium in the fade of the potassium release response in the rat parotid gland.

Abstract

The 86Rb release response in the parotid due to .alpha.-adrenergic (epinephrine), muscarinic (carbachol) or peptide (Substance P) receptor activation exhibited fade, a return of efflux to control levels despite the continuing presence of agonist. The time course of fade of the response to all 3 agonists was independent of the concentration of the agonist. After fade was fully developed to 1 agonist, the response to an agonist acting on a different receptor was either absent or greatly diminished. Removal of carbachol from muscarinic receptors with atropine 10 min prior to Substance P partially restored the ability of Substance P to produce a response. Fade of the response with all 3 agonists was greatly retarded by the omission of Ca. Release of .alpha.-amylase did not appear to fade following exposure to carbachol or Substance P. The K+ release response may be inactivated with time due to diminution in responsiveness of the K+ channel to an increase in internal Ca2+.