Youko Satow

The effect of sodium on “Paranoiac”—A membrane mutant of Paramecium

Abstract o 1. A behaviorally “paranoiac” strain of Paramecium is studied electrophysiologically and biochemically. When bathed in Na + solutions, the mutant shows prolonged excitation up to 60 sec. 2. The duration and plateau level of the prolonged depolarization are proportional to the [Na + ] out . 3. Test show that the membrane is highly conductive during the depolarization. 4. Flame photometry shows up to 70% loss of internal K + . This loss, not observed in wild type, is proportional to [Na + ] out . 5. 22 Na analyses show a large gain of Na + by the mutant proportional to [Na + ] out . 6. We conclude that the mutation-prolonged depolarization represents an otherwise normal excited state where conductances of K + and Na + are high.

Mutants with reduced Ca activation inParamecium aurelia

SummaryTwo heat-sensitive “pawn” mutants ofParamecium aurelia are capable of avoiding reactions when grown at 23°C but not at 35°C. Electrophysiological analyses show that Ca activation is reduced in the mutants even when they are grown at 23°C. The maximal rate of rise and the peak of the evoked action potential (Ca-spike) in the mutants are smaller than those of wild type in a K-solution. After suppression of K conductance by either TEA+ or Ba++, the action potentials of the mutants peak at the same level as that of wild type. However, the maximal rate of rise of the mutants remains only about half that of wild type. Thus, the mutations affect Ca activation but not K activation.Incubation at a high temperature (35°C) further reduces Ca activation to almost zero in the mutants but has little or no effect on wild type. This almost complete loss of Ca activation explains the lack of avoiding reactions when the mutants are grown at high temperatures. A double mutant containing two heat-sensitive mutations shows extremely reduced Ca activation even when grown at 23°C.

Possible Reduction of Surface Charge by a Mutation in Paramecium tetraurelia

SummaryUnder voltage clamp, a mutant ofParamecium tetraurelia (teaB) shows a shift in the positive direction of the voltage sensitivity of the Ca conductance and the depolarization inactivation curve by 10 mV with no change in the total conductance. This effect can be mimicked in the wild type by the addition of external Ca2+ or Mg2+. The mutation also shifts the resting potential and the voltage sensitivities of the delayed rectification (depolarization-sensitive) K conductance and the anomalous rectification (hyperpolarization-sensitive) K conductance in the positive direction to a similar extent. This systematic shift of channel voltage sensitivities is best explained by the reduction of the surface negative charges of the membrane due to the mutation.

A regenerative hyperpolarization inParamecium

SummaryA regenerative hyperpolarization is recorded from the membrane ofParamecium tetraurelia in a Ca solution (Fig. 1). This hyperpolarizing response, triggered by injected inward currents, has a threshold near −60mV and reaches a minimum of about −120mV (Figs. 2, 3). Membrane resistance is much smaller during this response than at rest (Fig. 4). Externally applied K+ or TEA+ inhibits this regenerative response (Figs. 6, 8). Internally applied TEA+ inhibits (Fig. 9) and internally applied K+ facilitates (Fig. 7) this response. These results show that the regenerative hyperpolarization is due to a K efflux and goes toward the Ek. This hyperpolarizing response (called “K-spike”) can be triggered by mechanical stimulation at the posterior region of the cell (Figs. 10, 11). The Ca++ effects and the behavioral consequence of this “K-spike” are discussed.

Effects of K+, Ba2+ and Ca2+ on the excitable membrane in Paramecium tetraurelia

Abstract 1. 1. The effects of Ba2+ and K+ ions on the membrane currents of Paramecium tetraurelia under a voltage clamp were investigated. 2. 2. External Ba2+ suppresses the inward-going K-current and the Ca-induced K-outward current and changes the activation and inactivation kinetics of transient inward current through the Ca-channel. 3. 3. K+ increases the Ca-induced K-conductances but little affects the leakage conductance. 4. 4. The resting potentials by changing those ionic concentrations shift the voltage sensitivities of all voltage sensitive channels, simultaneously. 5. 5. The competition between ions to the channel responses was discussed.