EFFECT OF POTASSIUM ON THE MECHANICAL ACTIVITY OF TAENIA COLI, UTERUS AND PORTAL VEIN OF THE GUINEAPIG

The effect of solutions containing 5·9 to 127 mmol.l −1 potassium on the mechanical activity of taenia coli, uterus and portal vein of the guinea‐pig was investigated using isometric and isotonic recording in vitro . In the taenia coli at 37°C an increase of the K + ‐concentration from 5·9 (Krebs' solution) to 6·4 or 6·9 was sufficient to elicit mechanical activity. Maximal contractures were obtained with about 24 mmol.l −1 K + , both with isometric and isotonic recording (in the latter case with loads ranging between 1 and 7 g). With higher K + ‐concentrations the contractures were not greater or were slightly smaller. In the taenia coli at 37°C the isometric contractures were well maintained (up to 15 min) when obtained with 20‐40 mnmol.l −1 K + . With higher K+ ‐concentrations the tension declined after 30–60 s, the more noticeably the higher the K+ ‐concentration. At 18°‐21°C the decline in tension during K + ‐stimulations started earlier in time, occurred with lower K + ‐concentrations, and was more noticeable. However, even at 15°C K + ‐concentrations of about 22–30 mmol.l −1 produced contractures maintained up to 15 min. Isotonic contractures were always better maintained than isometric contractures. Solutions containing over 25 mmol.l −1 K + produced at 37°C an initial transient relaxation of the taenia coli, which was abolished by tetrodotoxin but not by guanethidine or atropine; it was also present after the adrenergic fibres had been destroyed by 6‐hydroxy‐dopamine. It is suggested that this relaxation is due to stimulation of non‐adrenergic inhibitory nerves. A transient relaxation was also observed when the K + ‐concentration was raised during a spontaneous contraction or during stimulation with carbachol. In the uterus maximal contractures were obtained with K +‐concentrations of 20–30 mmol.l −1 ; smaller contractures were obtained with higher K+ ‐concentrations. With K + ‐concentrations up to 45 mmol.l −1 the isometric contractures were well maintained; with higher K + ‐concentrations they declined within 30‐90s. Isotonic contractures were better maintained than isometric contractures. In taenia coli and uterus after stimulation with solutions containing more than 50 mmol.l −1 K + upon re‐introduction of the Krebs' solution there were powerful contractions (after‐contractions) which lasted longer the higher the K + ‐concentration had been. In the portal vein the isotonic contractures were approximately proportional to the K + ‐concentration.