[The modification of potential-dependent calcium channels in the membrane of secretory cells in a calcium-free medium].

Effect of modification of potential-dependent calcium channels in cells of the upper lobe of the salivary gland in Chironomus larva has been ascertained in the Ca-free medium containing Ca-binding substances (EGTA or EDTA). It is shown that the inward current depends on the sodium transmembrane gradient. The amplitude of the inward sodium current decreases under the influence of verapamil as well as with an increase of external concentration of Ca2+ ions. The metabolic dependence of modified calcium channels as well as the pharmacological sensitivity are unchanged. Tau n of the sodium current through modified calcium channels increases insignificantly comparing with that of the calcium current. Maximum of the current-voltage relationship of the sodium current through modified calcium channels is shifted to a negative side by 10-15 mV as compared with the calcium current through native channels.