MODULATION BY ALBUMIN OF NEURONAL CHOLINERGIC SENSITIVITY

Bovine serum albumin greatly enhanced the cholinergic response mediate d by neuronal nicotinic acetylcholine receptors in chick ciliary gangl ion neurons. The enhancement exceeded 5-fold in some experiments (mean +/- standard error, 3.26 +/- 0.43-fold) and was rapid, was dose depen dent, and occurred without changes in the unitary conductance or the m ean open time of the acetylcholine receptor channel. This lack of dete ctable change in permeation or kinetic properties suggests that bovine serum albumin might increase acetylcholine responses by increasing th e number of functional receptors. The enhancement appears to be specif ic to the albumin molecule, because activity could not be removed by d etergent extraction, gel filtration, or dialysis. Acetylcholine respon ses in these cells are known to be enhanced by a cAMP-dependent mechan ism that converts existing acetylcholine receptors from a nonfunctiona l to a functional state. We found that the enhancement by bovine serum albumin occurred without an increase in cAMP and that pretreatment wi th membrane-permeable cAMP analogs prevented any additional enhancemen t of the cholinergic response by bovine serum albumin. These observati ons are consistent with a cAMP-dependent modulation of the enhancement produced by bovine serum albumin or a convergence of the two enhancem ent mechanisms onto a single pathway