[The myogenic basis of smooth muscle motility (author's transl)]

Differentiation of the action potential in the smooth muscle of canine gastric antrum using calcium-inhibitory drugs

Electrical and mechanical activity were recorded simultaneously in smooth muscle preparations from the antrum region of canine stomach by means of a single sucrose gap technique (SGT). The SGT was optimized to permit stable recording from multicellular smooth muscle preparations over several hours of electrical and mechanical activity with little disturbance of their normal properties. Acetylcholine (ACh, 10(-8) to 10(-6) M) induced or augmented dose-dependently the electrical and mechanical activity. The plateau of the action potential complex was elevated by ACh, while the contraction was increased in linear correlation to the magnitude of the plateau component. In spontaneously active (or in ACh-stimulated) preparations TEA (5 to 20 mM) magnified the plateau component, induced or strengthened spikes on the plateau ('secondary spikes'), and induced or strengthened phasic contractions. Nifedipine (10(-6) M) abolished secondary spikes, part of the plateau component of the action potential, and suppressed mechanical activity. The complex action potential of canine gastric antrum can be differentiated into (a) a basic action potential, consisting of an initial, primary spike and a plateau depolarization; this basic action potential is resistant to nifedipine and does not trigger any mechanical activity; and (b) a nifedipine-sensitive component (calcium component), which consists of an augmentation of the plateau depolarization and of secondary spikes, and which is responsible for the initiation of mechanical activity.

Differentiated contractile responses of gastric smooth muscle to substance P

Muscle strips were excised from the circular and longitudinal layers of the fundus, corpus and antrum of canine stomach, and from the inner portion of the pyloric ring (inner pylorus). Substance P (SP) induced strong contractions, with the greatest sensitivity in fundus and circular corpus preparations (threshold near 10 -10 mol/l). The sensitivity to SP decreased in the sequence circular corpus - longitudinal antrum - circular antrum (threshold near 10(-7) mol/l); it re-increased towards the pylorus, and in the inner pylorus was nearly as high as in the fundus. The SP responses of fundus and longitudinal corpus were purely tonic, similar to acetylcholine (ACh) and histamine (H) responses. In circular corpus, SP induced a combined phasic-tonic response. SP induced in antrum strips purely phasic-rhythmical contractions of low frequency (similar to the H response), whereas ACh induced phasic contractions of high frequency, and in addition an increase of tone in the longitudinal antrum strips. The SP responses of the inner pylorus were not uniform; in some preparations purely tonic contractions were observed, and large phasic fluctuations of low frequency occurred in others. The phasic components of all the responses were completely suppressed by nifedipine (10(-6) mol/l). Tetrodotoxin as well as blockade of adrenoceptors, of ACh and of H receptors had no effect on the SP responses. Comparative studies with preparations from guinea-pig showed that species differences exist in the SP responses of gastric muscle.

Mechanical activity of isolated canine coronary arteries after coronary occlusion

Collateral vessels from dogs showed good mechanical responses, with well-developed inhibitory responses, for example to noradrenaline. Endogenous inhibitory processes, which resulted in a low spontaneous basal tone, were also well-developed in most tissues. However, signs of hyperactivity were observed in some cases - and this might be the most interesting result. This hyperactivity was characterized by a strong phasic spontaneous activity. This might be an abnormality associated with the rapid proliferation of smooth muscle cells in collateral vessels. It is quite possible that such states of hyperactivity may play a role in human pathology, Producing coronary spasm and leading to angina or infarction, perhaps even in hearts with well developed collaterals.

The effect of lysolecithin on contractile force of isolated gastric smooth muscle

Mechanical activity of smooth muscle preparations was recorded in circular strips of antrum, corpus, and fundus from guinea-pig stomach. Whereas acetylcholine stimulated both rhythmic and tonic (shift of the base line) activity of the tested muscles, lysolecithin induced tonic contractions, but had no influence on the rhythmic activity. Lysolecithin was ineffective in the absence of external calcium. The tonic activations of corpus and fundus preparations induced by lysolecithin were suppressed by sodium nitroprusside. D 600 (methoxy-verapamil) did not counteract the lysolecithin effect.