Asymmetric Divergence in Structure and Function of HCN Channel Duplicates in Ciona intestinalis
Figure 4
Potassium passes through both Ciona HCNs and enhances current flowing through them.
A. Current traces elicited by a multi-step protocol in oocytes expressing either Ciona HCN isoform to obtain instantaneous Ih versus voltage relationship, carried out in low and high concentrations of extracellular potassium. The voltage protocol is shown below the current traces. The first set of voltage pulses allow for the determination of instantaneous current at each test voltage; the second set of pulses allows for the determination of total instantaneous current at each test voltage, following Ih activation at a potential at which the current is close to fully activated. Subtracting the latter from the former yields the total instantaneous Ih at each test voltage. B. Plots of instantaneous Ih amplitude versus test voltage at low and high concentrations of extracellular potassium as determined in ‘A’. Values represent mean ± s.e.m. at each test voltage; light gray/squares for low 5 mM K+, dark gray/circles for 10 mM K+, and (black/triangles) for 96 mM K+. C. Bar graphs showing the reversal potentials and slope conductance for each ciona HCN in different concentrations of potassium; these were determined from experiments in ‘A’ where values from individual experiments were fit by a straight line through the linear portion of the curve across the x-axis. The number of oocytes that were used in each group is shown above each bar in brackets; reversal potential and slope conductance were obtained from the same current data. Values represent mean ± s.e.m. for each potassium concentration. Statistical significance was determined using a one-way ANOVA and post-tukey multiple comparison test. * indicates difference between 96 mM potassium (p<0.05) and 5 mM and # indicates a difference between 96 mM potassium and 10 mM potassium (p<0.05). Light gray, dark gray and black bars represent values for 5, 10 and 96 mM potassium.