Abstract
I. Action of spasmogens. Evidence has been obtained suggesting that (1) for all of the spasmogens (K, ACh, Ba) tested, phasic contraction is produced by Ca release while tonic contraction is maintained by the energy-dependent influx of Ca. (2) Only in case of Ba, is a direct stimulation to the contractile protein of muscle partly concerned with contraction. This is implied by a residual contraction by Ba in the Ca-free bath solution. (3) Ba releases Ca from the store of easily releasable Ca, as K and ACh, and in addition from the store of less easily releasable Ca. II. Action of antispasmodics. As the result of various experiments, it was concluded that (1) antispasmodic action of isoproterenol is attributed to the depression of muscle cell membrane, that is, due to the pseudo-competitive (or functional) inhibition of release and then influx of Ca with increased concentrations used. (2) Antispasmodic actions of papaverine and chlorpromazine are attributed to the depression of membrane (competitive inhibition of influx and then release of Ca) followed by a non-competitive inhibition against the contracting action of Ca on the muscle contractile system with increase of concentrations.
