Search

Action potentials (AP) of neurons A and B could be only elicited in the presence of Na-+ ions. An increase in [Ca-++]0 led to depolarization of neurons, enhancement of their excitability, AP, overshoot, of positive afterpotential, AP duration, AP maximal rate of fall (Vf) and to decrease in AP maximal rate of rise (Vr). After addition of CaCl2 up to 50 mmoles into the Ringer solution, the membrane resistance (R) increased. If the [Na-+]0 was equimolarly diminished, R increased up to the [Ca-++]0 30 mmoles, but at greater [Ca-++]0 R fall below the initial value. The regularities were independent of the initial value of resting potential (RP). At high [Ca-++]0 Ca-++ contributed to the generation of the inward current during AP while Na-+ caused an increase in ionic (calcium) membrane permeability at rest. At high [Ca-++]0, Na-+ was also necessary for support of membrane channels which maintained the inward and outward currents during the AP.

Chlorcholine chloride (CCC) the molecule of which has no other group, characteristic of acetylcholine (Ach), causes an effective cholinomimetic action on the surface membrane of the mollusc neurons A and B. As the concentration of Ach and CCC increases from 10(-6) to 10(-3) M the resting potential (RP) and the membrane resistance (R) of the neuron A first increases then decreases. The increase of Ach and CCC concentration causes in the neuron B only a decrease of the above mentioned parameters. The data point to the necessity of improving the ideas about the structure of cholinoreceptors and mechanism of cholinoreceptor-cholinomimetic interaction.