Inactivation of calcium channels.

Rapid progress in our understanding of the properties and functions of voltage-gated calcium channels had produced the need for an update to our previous review of calcium inactivation. The major elements of change included in this review are: 1. The existence of multiple forms of voltage-sensitive Ca+ channels, with distinctive single channel properties, thus necessitating a reappraisal of properties deduced from macroscopic current recordings, particularly of the processes of activation and inactivation. 2. The differences in biochemical properties between channel types are reflected in their differences in divalent selectivity, their requirement for metabolic maintenance and their mechanism of inactivation. These properties appear to divide the channels into two categories which may relate to their molecular structures. Further subgroupings, based upon the voltage thresholds, have also been observed. 3. Molecular properties of one class of channels have been elucidated, which correlate with the observed biochemistry of channel modulation and inactivation. 4. An enzymatic process underlying the mechanism of Ca2+-dependent inactivation has been elucidated and may serve as a model for other modulatory systems. The interweaving of the properties of these Ca2+ channels, with their spatial distributions and their influence upon other channel types, acts to transduce and integrate information within cells.