Calcium ions have the ·important roles in the variouE processes in muscle contraction. Especially extracellular calcium as a source of calcium for contrartion is decisive in cardisc muscle contraction because slow calciun inward current during depolarization of sarcolemma deternlines the calcium concentration in sarcoplasm.
It is well known that hydrogen ion has the negative inotropic effect on cardiac muscle. Although the precise meclnlnism of hydrogen ion on cardiac contractility if uncertain, its effect on cardiaccontractility is closely related to the action of calcium.
The potassium ion also has a negative inotropic effect and its mechanism on cardiac contractility has not been established. Furthermore, the contractility is not known.
The author intended to investigate the effects of concurrent changes in pH and calcium concentration, pH and potassium concentration on ventricular contactllity.
For these purpose, combination of each changes either in pH 8.4, 7.4 and 6.4, i. e. 1 unit det·iat-ion from normal pH, with the calcium concentration of 1, 2, and 4 mM/L, or potassium confentration of 0.5, 2, and 6mM/L was chose for ventricular perfusion.
Turtle heart was selected for experiments and Langendorf´s Preparation for ventricular per-fusion was used. The perfusate was Tris buffered Ringer containing with different electrolyte concentration according to each group.
Tension and max. dT/dt as parameters of contractility were recorded by means of physiograph and its accessories.
The results are summarized as follows;
1. Increased pH exhibit the positive inotropic effect, While in decreased pH the negative inotropic effect on cardiac ventricle was observed.
2. In each pH of 8.4, 7.4, and 6.4, the increased calcium concentration enhanced the ventricular contractility while decreased calcium concentration inhibited the cardiac contractility.
3. With those pH of 8.4, and 6.4, the changing rate of ventricular contractility according to changes of calcium concentration were similar to those with pH 7.4.
4. On the other hand, those with pH of 8.4, 7.4, and 6.4, with increased potassium concentration exhibited the negative inotropic effect and decreased potassium concentration enhanced the tension and male. contraction dT/dt but decrease in max. relaxation dT/dt.
5. With pH of 8.4, the changing rates of contractility according to changes with potassium concentration were similar to that of pH 7.4, while those with pH of 6.4. it was lower thanthat at pH 7.4.
6. The correlation between % change in malt dT/dt and ff cHange in tension was statistically significant belt·eon the contractility change according to pH changes alone and simultaneouschanges in pH and calcium concentration.
7. In the case of concurrent changes in pH and potassium concentration, the correlation between % changes in max. contraction dT/dt and 8 change in tension was statistically significant, however that between % changes in max. relaxation dT/dt and T change in tension was not remarkable.
From the above results, it is suggested that effects of pH on the action of calcium in ventricular contractility is different from that of potassium.
|