Binding of Acetylcholine

Abstract

Maximum stability of the bound acetylcholine (ACh) in brain suspensions is found at about pH 7. The rate of breakdown increases rapidly above pH 8 and below pH 6. The rate of breakdown of bound ACh in brain is greatly accelerated, especially initially, by suspension in hypo-tonic medium and by high concns. of K, Ca or Mg ions. The presence of eserine seems to decrease the breakdown appreciably. The increased ACh content of normal brain slices incubated aerobically in the presence of glucose is accounted for mainly by bound ACh. But the greatly increased ACh content of slices incubated in medium containing free ACh, previously reported, is only to a small extent actually bound. It is largely accounted for by free ACh within the slice, which is not readily rinsed out. The bound ACh in brain suspensions is increased by the presence of ACh (30 [mu]g./ml.) in the medium. Heart and skeletal muscle suspensions bind ACh slightly. No binding was detected with liver, kidney or testis suspensions. Convulsant and narcotic drugs tested (other than ether) exerted no effects on liberation or binding of ACh by brain suspensions.