Scaling of recovery rates influences T-type Ca(2+) channel availability following IPSPs

The excitability of neuronal membranes is crucially modulated by T-type Ca(2+) channels (I(CaT)) due to their low threshold of activation. I(CaT) inactivates steeply at potentials close to the resting membrane potential. Therefore, the availability of I(CaT) following changes in membrane potential depends on the time course of the onset of inactivation as well as on the time course of recovery from inactivation. It was previously shown that the time course of recovery from inactivation depends on the duration of the conditioning pulse in cloned T-type Ca(2+) channel subunits (Ca(v)3.1-Ca(v)3.3(Uebachs et al., 2006)). This provides a potential mechanism for an intrinsic form of short term plasticity. Here, we address the question, whether this mechanism results in altered availability of I(CaT) following physiological changes in membrane potential. We found that the recovery of I(CaT) during an IPSP depends on the duration of a preceding depolarized period.