Voltage and pharmacological modification of membrane currents during the action potential in Chara inflata

摘要

The transient inward, I_(i(max)) and the delayed outward I_((max)) currents in C. inflata were triggered in an all-or-none fashion. At a test potential of —60 mV a clamping duration of 100 ms to 250 ms was sufficient to trigger the transient inward current and stop the cytoplasmic streaming. The reversal potentials deduced from the current-voltage relations of the components indicate that the transient inward, I_(i(max)), was carried by Cl~- and the delayed outward, I_((max)) by K~+. The negative prepulse enabled reproducibility of I_(i(max)) and I_((max)). TEA~+ (tetraethylammonium) induced action potentials in C. inflata and hyperpolarized the free running membrane potential, V_m, in C. corallina. In voltage-clamp experiments, TEA~+ blocked I_(i(max)) and increased I_((max)). In the hyperpolarized state, 1 mM 9-AC (9-anthracenecarboxylic acid), a Cl~- channel blocker, prevented the NaCl-induced depolarization in V_m, hyperpolarized the V_m by —20 to —40 mV and increased the membrane resistance.