Calcium channel stability measured by gradual loss of excitability in pawn mutants of Paramecium aurelia.

Mutants of Paramecium aurelia that are unable to reverse swimming direction are called pawns. They lack the inward ionic (calcium) current required for the upstroke of the electrically excitable membrane response. By following the progressive loss of reversal response and excitability in cells that are suddenly changed from a heterozygous (wild-type) state to a homozygous mutant state, an estimate of the stability and mean lifetime of the calcium channel has been obtained. During rapid growth, channel dilution due to division occurred, but no channel decay was observed. Under conditions of slow growth, decay could also be observed; channel lifetime was found to be from 5 to 8 days.