VOLTAGE-DEPENDENT AND CA2-DEPENDENT OF THE K+ CHANNEL IN THE VACUOLARMEMBRANE OF CHENOPODIUM-RUBRUM L SUSPENSION CELLS()

Voltage- and Ca2+-dependence of the slow-activating SV-K+ channel in t he vacuolar membrane of Chenopodium rubrum suspension cells has been a nalyzed using the patch clamp technique in the vacuole-attached, outsi de-out and whole-vacuolar configuration. Patch-pipette perfusion was a pplied to measure Ca2+ dependence of single channels in the attached-c onfiguration. Using the PCLAMP-software (Axon Instruments), an algorit hm was developed to extract reliable individual channel data from mult i-channel activity records, including open probability, mean open and closed times, as well as time constants for open and closed distributi ons. The channel conductance of the major open state was about 83 pS ( seal resistance > 8 G Omega) at 30 mV (transmembrane voltage V-m, vacu ole negative), and symmetrical 100 mM KCl. The channel exhibited a str ong voltage- and a weak Ca2+-activation: increasing V, from 40 to 100 mV is equivalent to a Ca2+ concentration change from 10(-7) to 10(-4) M. Mean open probabilities at V-m = 30 mV were 0.03 with 1 mu M and 0. 09 with 100 mu M Ca2+. Mean open times were approx. 7 ms. and almost i ndependent of both, voltage and Ca2+. Mean closed times, however, vari ed in a strongly voltage- and Ca2+-dependent manner, e.g., at V-m = 30 mV dropped from 205 to 67 ms, if Ca2+ was raised from 10(-6) to 10(-4 ) M. Open and closed distributions of events within bursts could be fi tted by the sum of two exponentials with time constants between 0.3 an d 11 ms.