Membrane currents and evoked calcium transients.

A–Sample HCN and calcium currents evoked by voltage steps to -50 and -110 mV, respectively, from the holding potential -70 mV, close to the measured resting potential. CA1 neurons were intracellularly dialyzed with intracellular solution containing Cs+ + TEA (see Methods). Under these conditions depolarization-evoked calcium currents (upper panel, the voltage steps to >-60 mV) and hyperpolarization-activated HCN currents (lower panel, the voltage steps toB–HCN currents in WT (blue) and RTT (violet). Note smaller amplitude and slower time-course in RTT cells. C–Potential dependence of activation. The curves were obtained from the tail currents and normalized to maximum (left). The half-rise times (t1/2) are shown in the right panel. The differences can be attributed to decreased cAMP levels in RTT [25, 28]. D–Calcium transients during membrane depolarization. The traces indicate calcium changes measured with fluo-4 (100 μM in the pipette) evoked by the voltage step protocols schematically shown under the traces. E–Differences in the voltage-evoked calcium transients. Depolarization to 0 mV for 1 s evoked calcium increases in WT CA1 neurons (blue) that were smaller and faster than those in RTT cells (violet). Subsequent decay to the resting level was described by a single exponential in WT and in RTT an additional slower exponential appeared (the values are listed near the respective curves).