[Characteristics of potential-dependent calcium channel current of the secretory cell membrane].

The parameters of inward current of potential-dependent calcium channels in cells of the upper and lower lobes of the salivary glands in Chironomus larvae have been studied. The current activation thresholds in cells of both types are near -60 mV, but in cells of the upper lobe the current reaches its maximum values at -20 mV, while in cells of the lower lobe at -10 mV. The current density in cells of the upper lobe is approximately 1.3 times higher and the inactivation time constant is 1.62 less than in cells of the lower lobe. Calcium channels in cells of the upper and lower lobes of glands also differ in metabolic dependence: introduction of cAMP, ATP and Mg2+ into cells of the lower gland lobe causes a considerable increase in the current amplitude, while the same action in cells of the upper lobe--its decrease. The current amplitude in the cells of the lower lobe decreases under the influence of nitrendipine and La, Co, Ni, Cd, Zn cations as well as a decrease of the temperature or pH in the external solution.