8.Effect of extracellular pH and Ca++ - concentration on the contractility and force generation as verified on Vorticella stalk concentration pattern
Amit Kumar Verma and Ashok Kumar Singh
The prediction of protoosmotic model (as in actin-myosin system) has been applied to pattern of Vorticella stalk contraction for its verification. Vorticella stalk contraction is effected by the neutralization of negative charges at the end of spasmin by Ca++. ATP hydrolysis is only required to sequester the cytosolic Ca++. The effect of pHs in both acidic and alkaline ranges on the stalk contraction pattern was examined in combination with different Ca++ concentrations to characterise the contraction mechanism. By increasing H+ concentration the frequency of contraction decreases consistently. No change is found in duration of contraction. On returning to normal pH the same frequency of contraction is resumed. The effect of acidic pH thus is reversible. By lowering the H+ concentration (pH 8.0 and above) frequency of contraction becomes faster and the duration of contraction also improves compared to the duration at neutral pH. In triton–extracted preparation the contraction is found only at neutral pH for sometimes. No discernible change in contraction is found at changing pH. At both lower and higher pHs the change in Ca++ concentrations (from 1 mM to 4 mM) make pronounced effect. The results conformto other biological motile apparatus.