Membrane capacitance

 a. Explain what membrane capacitance is.  [1]

b.  During a depolarizing voltage step, will the capacitative current by inward or outward? [1]

3. The raw traces (A) show Ca2+ currents in a cell treated with either DMSO (the control vehicle solution) or PMA, a compound that activates an intracellular molecule: Protein Kinase C (or PKC).

A C fast-phase ETP DMSO HP-60 mv -25 100 nM PMA 40 DVSO VC 200 PA PMA 20 ms 20 ms B vollage (mV) -40 -20 20 10 D 0- fast T -0,2- -DM50 (0=7) -PMA (n=0) peak amplitude (nA) 0.4- peak 0.6- CUTTen! (nA) -151 -0.B DMSO PMA Figure 8. Activation of PKC enhances bag cell neuron Cad current evoked by a waveform that mimics am electrotonic potential. A, Single bag cell neurons are bathed in Ca#+-C +-TEA ASW and treated with either DMSO or 100 mm PMA for 20-30 min before whole-cell voltage clamp using a ( *-Asp-based intracellular saline (inset). Stepping the neurons from a holding potential (HP) of -60 mV to 40 mV in 200 ms, 10 mV intervals, evokes a voltage-dependent Can’t current that is modestly inactivating during the test pulse. Compared with a neuron given DMSO (top), the current from a cell exposed to PMA (bottom) is three-fold larger. Scale bar applies to both traces. B, Plotting peak Cavi current against step voltage reveals a nonlinear, voltage-dependent relationship. The current is inward and peaks between Oand 10mV for both DMSO (dear cirdes) and PMA (black circles). Yet, the peak in PMA is significantly greater than DMSO at potentials more positive than -30mV (-30mV, fig) = 3404, "p <0.02; -20 my. for = ].106, "p <0.03; -10 mV, =3568, "p <0.02:0mV.1= 4369, "p <0.008: 10 my,figg =3.872, "p <0.02: 20mV, fg = 4.287, "p < 0.08:30mV, fig) = 4115, "p <001; 40 mV, fry = 3.744, "p < 0.02; all unpaired Student’s ( test). N values indicate number of individual neurons recorded following DMSO or PMA. (, A fast-phase ETP-like waveform (top] is given to single bag cell neurons voltage-damped at – 40 mV while recording Cat current. The waveform elicits an -200 pA current in a neuron treated with DMSO beforehand (gray trace; bottom). By comparison, a cell in PMA displays a two-fold langer Cad* current (black trace; bottom). Abscissa also applies to the top panel. D, The peak amplitude of the ETP-like waveform-induced Ca di current is significantly greater in PMA versus DMSO (fog = 3.353, "p <(007: unpaired Student’s /test). Avaluesindicate number of individual neurons recorded following DM50 or PMA.

. Are these raw Ca2+ currents (A) inward or outward? Explain why this is the case in terms of the electrochemical driving force. [2]

b. Does activation of PKC by PMA, inhibit or enhance the Ca2+ currents? How did you deduce this? [2]

c. When the currents from all cells were averaged and the current plotted in an I / V relationship (B), what is the approximate peak amplitude for a. DMSO-  b. PMA- treated cells? [2]

d. Why are the currents on the I/V relationship given negative values? [1]

e. According to the I/V relationship, at what potential is the inward current maximal for     a. DMSO,  b. PMA-treated cells? [2]

f. Based on the I/V relationship, would you say that activation of PKA:

        a. Enhances the peak Ca current by 50%

        b. Enhances the peak Ca current by 100%

        c. Enhances the peak Ca current by 30%

        d. Enhances the peak Ca current by 300%

        e. Reduces the peak current by 300%