3. A cell has the following conditions at rest (28 points) [Na], = 155 mM [Na] = 8 mM [Ca] = 1.5 mm [Ca] =0.3 μM [K], 6 mM [K"] =

150 mM a. Calculate En. Eca, and Ex b. If gx = 80 g, and gc. = 0.25 g, calculate Em at rest. c. Calculate the net driving force for Ise. Ik and Ica Hint: net driving force of an ion is En-E. d. Calculate the relative values of Isa. Ik, and Ica (you can leave ga as an unknown). In which direction would the current be flowing for each ion? e. What is the sum of the current produced by all the ions? What does this tell us about the membrane? f. A stimulus causes Ca channels to open, resulting in a sudden increase in Ca** conductance so that now gca = 10 ga. What is the new membrane potential? (Assume ion concentrations stay the same as at rest and Na* & K* conductance don't change) g. If the normal threshold for an action potential is -55 mV, is the stimulus in f enough to cause an action potential?