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Mechanical activity of the isolated portal vein and thoracic aorta of the guinea-pig was recorded and the effects of verapamil and D 600 (methoxy-verapamü) on the dose-response curves to noradrenaline were measured. Extracellular electrical activity in portal vein was also sometimes recorded. Two calcium activation mechanisms could be differentiated: a ‘spike activation mechanism’ (SAM) inhibited by verapamil and D 600, and a ‘spike-free activation mechanism’ (SFAM) resistant to these antagonists in their specific concentration range (up to 10^–5 mol/l). In portal vein, both mechanisms were similarly dependent on extracellular calcium, indicating a D 600-resistant system for transmembrane calcium fluxes. The response of portal vein to increased potassium concentration was also tested. Species differences and differences in the specificity of various calcium antagonistic drugs complicate the picture of calcium antagonism in vascular smooth muscle.

The mechanical activity of isolated strips from different areas of the pyeloureteral system was investigated in 10 pigs: calyx, renal pelvis, pyeloureteral junction and ureter. Additionally, electrical activity was measured in some pyeloureteral preparations using the sucrose-gap technique. Regular spontaneous activity with an average frequency of 9.5/min was recorded in calyceal strips, decreasing to 5.4/min in renal pelvis, 5.7/min in pyeloureteral preparations and to 1.2/min in ureteral preparations. The activity of renal pelvis, pyeloureteral and ureteral preparations was less regular, and bursts of fast activity (near 10/min) could be observed in all these preparations. The membrane potential of pyeloureteral strips showed spontaneous generator oscillations of about 10/min. Variations in the pattern of ureteral peristalsis are due to different coupling ratios of membrane potential oscillations to contractions. Adrenaline (10^––5 mol/l) increased the frequency of the oscillations and enhanced their manifestation in the mechanical recordings, whereas tetraethylammonium (5–20 mmol/l) only increased the coupling ratio. The following concept for the generation of ureteral peristalsis in multicalyceal kidneys is developed: several (primary) oscillators exist in the calyces; in the pyeloureteral junction a (secondary) pacemaker exists which has an intrinsic frequency similar to that of the calyceal pacemakers; both processes cooperate in the generation of ureteral peristalsis.