Slow inactivation of calcium channels

Voltage-gated calcium (Ca2+) channels open in response to membrane depolarisation and subsequently close. The process of channel closure is termed inactivation. Inactivation restricts Ca2+ fluxes into cells thereby regulating a vast variety of cellular processes such as electrical excitability, muscle contraction, gene expression and other events. Three inactivation subtypes have been identified in voltage-gated Ca2+ channels: Ca2+-dependent, fast voltage-dependent and slow inactivation (SI). The mechanism, molecular determinats and the physiological role of SI in Ca2+ channels are least understood. The present research project will, therefore, focus on the molecular determinants (i.e. identification of amino acids that either stabilise or destabilise SI), the underlying conformational changes, the biological role and the pharmacological relevance of SI in Ca2+ channels. In order to analyse its physiological role we will estimate the entry rates of different Ca2+ channel families into slow inactivation in heterologous expression systems (Cav1.2, Cav1.3, Cav2.1, Cav2.3) as well as in native cells and also study the recovery process (see Sokolov et al. 2000 for methodological details). This approach will enable new insights into the regulatory role of SI in tissue specific Ca2+ homeostasis. The analysis of slow inactivation in familial hemiplegic migraine (FHM) Cav2.1 mutants will enable a better understanding of the aetiology of this ion- channel-related pathology. The slow-inactivated Ca2+ channel conformation is - in analogy to the action of local anaesthetics in sodium channels - suspected to represent a prime target for Ca2+ antagonists. An analysis of drug effects on our Ca2+ channel mutants with changed SI properties will, therefore, help to clarify this pharmacologically important question on a molecular level.

Voltage-gated calcium (Ca2+) channels open in response to membrane depolarisation and subsequently close. The process of channel closure is termed inactivation. Inactivation restricts Ca2+ fluxes into cells thereby regulating a vast variety of cellular processes such as electrical excitability, muscle contraction, gene expression and other events. Three inactivation subtypes have been identified in voltage-gated Ca2+ channels: Ca2+-dependent, fast voltage-dependent and slow inactivation (SI). The mechanism, molecular determinats and the physiological role of SI in Ca2+ channels are least understood. The present research project will, therefore, focus on the molecular determinants (i.e. identification of amino acids that either stabilise or destabilise SI), the underlying conformational changes, the biological role and the pharmacological relevance of SI in Ca2+ channels. In order to analyse its physiological role we will estimate the entry rates of different Ca2+ channel families into slow inactivation in heterologous expression systems (Cav1.2, Cav1.3, Cav2.1, Cav2.3) as well as in native cells and also study the recovery process (see Sokolov et al. 2000 for methodological details). This approach will enable new insights into the regulatory role of SI in tissue specific Ca2+ homeostasis. The analysis of slow inactivation in familial hemiplegic migraine (FHM) Cav2.1 mutants will enable a better understanding of the aetiology of this ion- channel-related pathology. The slow-inactivated Ca2+ channel conformation is - in analogy to the action of local anaesthetics in sodium channels - suspected to represent a prime target for Ca2+ antagonists. An analysis of drug effects on our Ca2+ channel mutants with changed SI properties will, therefore, help to clarify this pharmacologically important question on a molecular level.