FIG. 4.

Effects of heterologous Gem expression on N-type Ca²⁺ and M-type K⁺ channels of sympathetic neurons. (A) Current-voltage relationships for Ca²⁺ currents (I_Ca) recorded from a control neuron (uninjected; open circles) and one injected approximately 24 h earlier with Gem cDNA (filled triangles). The inset illustrates superimposed I_Ca traces evoked by a 70-ms voltage step to +13 mV from a holding potential of −80 mV. Calibration bars, 20 ms (horizontal) and 0.3 nA (vertical). (B) Average I_Ca density (± SEM) in uninjected neurons (open bar) and neurons injected with wild-type (wt) or mutant Gem cDNA (filled bars) as indicated. I_Ca density was calculated from the I_Ca amplitude at a test pulse of +10 mV normalized to cell membrane capacitance. (C) Representative current traces of the K⁺ current arising from M-type channels (I_M) recorded from a control neuron (left) and a neuron previously injected with Gem cDNA (right) in the absence (control) or presence of 10 μM OXO-M. I_M amplitude was measured as the difference in current magnitude between the beginning and end of a 500-ms hyperpolarizing voltage step to −60 mV (arrows). (D) Average I_M density (± SEM) measured from control neurons (open bar) and neurons previously injected with Gem cDNA (filled bar). I_M density was determined by normalizing I_M amplitude (see above) to membrane capacitance. (E) Average percent inhibition (± SEM) of I_M produced following OXO-M (10 μM) application in control neurons (open bar) and neurons previously injected with Gem cDNA (filled bar). Number of neurons tested is shown in parentheses. **, P < 0.01.