Voltage-Gated Calcium Channels

1. Voltage-Gated Calcium Channels Dr. Ren-Zhi Zhan Institute of Physiology Shandong University School of Medicine E-mail: zhan0001@sdu.edu.cn

2. Contents Classification of voltage-gated calcium channels Structures of voltage-gated calcium channels Functions of voltage-gated calcium channels

3. What Are Ion Channels? • Ion channels are ion-permeable pores in the lipid membranes of all cells • Ion channels open and close in response to stimuli, gating the flow of specific ions • The ions flow downhill thermodynamically • http://www.scholarpedia.org/article/Ion_channels

4. ion-permeable pores

5. Functions of Ion Channels • Setting up resting membrane potential in all cells • Excitability • Cell signaling • Excitation-contraction coupling • Excitation-secretion coupling • Fluid transport, volume regulation

6. Basic Properties of Ion Channels • Ion selectivity (离子选择性) • Gating (门控性)

7. Glossary Conductance（电导）:The ability of something (e.g. a wire or an ion channel) to pass current. Conductance (G) is measured in Siemens (S). Gating（门控性）:Conformational changes in an ion channel induced by an extrinsic source (i.e., voltage, ligands, stretch, etc.). Such conformational changes are responsible for functional properties like activation and inactivation.

8. Activation (激活): Opening of a channel due to the presence of a gating signal • Deactivation (去活): Closing of a channel due to removal of the gating signal (i.e. the opposite of activation) • Inactivation (失活): Closing of a channel in the continued presence of the gating signal. The term "inactivation“ is usually only applied to voltage-gated channels, whereas "desensitization" describes the analogous process for ligand-gated channels. Once in the inactivated state, the channels can only be reopened by re-polarization to hyperpolarized membrane potentials, allowing the voltage sensor to return to its original closed conformation and the inactivation machinery to return to its de-inactivated position. • Desensitization (脱敏感化): Closing of a ligand-gated channel despite the presence of a bound activating ligand. For example, glutamate receptors desensitize in the continued presence of glutamate.

9. Tail current (尾电流): A current that flows during the repolarizing phase of an action potential or voltage command. K+ tail currents can be used to determine the reversal potential of voltage-gated K+ currents. In a physiological context, tail currents are often carried by Ca2+ ions and result from the increased driving force as the action potential repolarizes. • Access resistance (接触电阻): The electrical resistance between the inside of the patch pipette and the inside of the cell during a whole-cell recording. Compromises recordings by introducing a voltage-divider error and slowing the response time of the voltage clamp. Access resistance can be reduced by using larger patch pipettes and can be compensated electronically with the patch clamp amplifier.

10. Rectification（整流）: current passes in one direction better than it does in another

11. Types of Ion Channels • Voltage-gated ion channels • Voltage-gated sodium channels • Voltage-gated potassium channels • Voltage-gated calcium channels • Ligand-gated ion channels • Nocotinic acetylcholine receptors • GABAA receptors • NMDA/AMPA/kainate types of glutamate receptors • 5-HT3 receptors • Glycine receptors • miscellaneous • Mechanosensitive ion channels • Thermosensitive ion channels

12. Basic Structure of Voltage-Gated Calcium Channels Principal one alpha subunit and several auxiliary subunits The alpha subunit is responsible for basic electrophysiological and pharmacological properties The auxiliary subunits have regulatory roles Cain & Snutch,2010

13. Classification of Voltage-Gated Calcium Channels according to Physiological & Pharmacological Properties Cain & Snutch, 2010 Types L-Type: “L”for long-lasting N-Type: “N” for neuronal P/Q-Type: “P/Q” for Purkinje cells with question R-Type: “R” for resistant or residual T-Type: “T” for transient (only the T-type belongs to LVA)

16. Excitation-Contraction Coupling

17. Two Types of VGCCs Are Expressed in Cardiomyocytes Canine atrial myocytes Bean (1985) J Gen Physiol 86:1

19. VGCCs in the Heart

20. VGCCs and Neurotransmission

21. Synaptotagmin (突触结合蛋白) functions as a calcium sensor

22. Neurotransmitter release relies most on P-/Q- (Cav2.1) and N-type (Cav2.2) Ca2+ channels in the vast majority of neurons (Trends Neurosci 2003; 26 (12)) • P/Q-type channels are more frequently linked to excitatory transmission (Handbook of Experimental Pharmacology, volume 184) • In inhibitory synapses, P-/Q-type channels but not N-type channels are involved (Rev Neurosci 2012;23:179–190)

23. In fast inhibitory synapses, P-/Q-type channels but not N-type channels are involved Modified from J Neurophysiol 97:3567-3573, 2007.

24. Distribution and Functions of T-Type Calcium Channels • Increase in fidelity between presynaptic stimulation and post-synaptic response • Repetetive firing • Burst firing

25. Journal of Medicine and Life Vol. 4, 2011, pp.126-138

26. Cav3.1, Cav3.2 and Cav3.3 mRNA Levels in the Rat Brain

27. European Journal of Neuroscience, Vol. 24, pp. 2581–2594, 2006

28. T-Type Calcium Channels Support Burst Firing Neuron, Vol. 31, 35–45, July 19, 2001

29. L-cys – L-cysteine L-Ncys – L-nitrosocysteine Journal of Medicine and Life Vol. 4, 2011, pp.126-138

30. T-Type Calcium Channels amd Diseases • Mutation of T-type calcium channnels is associated with epilepsy in humans • Increased T-type calcium channel activity has also been linked to neuropathic and inflammatory pain states • Increases in T-type calcium channel expression are associated the development of epilepsy

31. Relatively Specific VGCC Blockers P/Q type: ω-agatoxin IVA (funnel-web spider, Agelenopsis aperta) N-type: ω-Conotoxins (MVIIA, CVID and GVIA) (cone snail Conus geographus) R-type: SNX-482 (tarantula) L-type: dihydropyridines cone snail Conus geographus (锥形螺） funnel-web spider, Agelenopsis aperta Tarantula (毛蜘蛛)

32. Where to Buy Calcium Channel Blockers • http://www.tocris.com • http://pepnet.com/ • http://www.alomone.com/

33. Big Questions • How does a channel selectively permit one ionic species to cross the membrane while excluding another? • How do VGCCs sense voltage? • How are ion channels regulated?