L-type Ca2+ CurrentsL-typeCa2+currents(longlasting)·high voltage of activationlargesingle-channel conductance,slowvoltage-dependentinactivation,markedregulationbycAMP-dependent proteinphosphorylation pathways,specific inhibition by Ca2+ antagonist drugs includingdihydropyridines,phenylalkylamines,andbenzothiazepinesaresubjectto regulation bysecond messenger-activatedproteinphosphorylationincardiacmyocytes,smooth,andskeletalmuscleinendocrinecellsinneurons
L-type Ca2+ Currents L-type Ca2+ currents (long lasting) high voltage of activation, large single-channel conductance, slow voltage-dependent inactivation, marked regulation by cAMP-dependent protein phosphorylation pathways, specific inhibition by Ca2+ antagonist drugs including dihydropyridines, phenylalkylamines, and benzothiazepines are subject to regulation by second messengeractivated protein phosphorylation in cardiac myocytes, smooth, and skeletal muscle in endocrine cells in neurons
T-type Ca2+ CurrentsT-type(transientkinetics)activate at much more negative membrane potentials(low-voltage-activatedCa2+currents)inactivate rapidlydeactivate slowlyhavesmallsingle-channelconductanceare insensitiveto Ca2+ antagonist drugsRegulationofT-typeCa2+currenthasnotyetbeenanalyzed in detail at the molecular levelinstarfisheggsinPurkinjeneuronsindorsal rootganglionneurons
T-type (transient kinetics) activate at much more negative membrane potentials (low-voltage-activated Ca2+ currents) inactivate rapidly deactivate slowly have small single-channel conductance are insensitive to Ca2+ antagonist drugs Regulation of T-type Ca2+ current has not yet been analyzed in detail at the molecular level in starfish eggs in Purkinje neurons in dorsal root ganglion neurons T-type Ca2+ Currents
N-type Ca2+ CurrentsN-typeCa2+currentsweredistinguishedbytheirintermediatevoltagedependence andrate of inactivation-more negativeandfasterthan L-type but more positive andslowerthanT-typeinsensitivetoorganicL-type Ca2+channelblockersbutblockedbytheconesnail peptide@-conotoxinGViAIndissociated dorsal rootganglion neuronsInneurons
N-type Ca2+ currents were distinguished by their intermediate voltage dependence and rate of inactivation–more negative and faster than L-type but more positive and slower than T-type insensitive to organic L-type Ca2+ channel blockers but blocked by the cone snail peptide -conotoxin GVIA In dissociated dorsal root ganglion neurons In neurons N-type Ca2+ Currents
P, Q and R-type Ca2+ CurrentsP-typeCa2+currentsfirst recordedinPurkinje neurons·high sensitivity to the spider toxin o-agatoxin IVAQ-typeCa2+currentsfirst recorded in cerebellar granule neuronsblocked by @-agatoxinIVAwith loweraffinityR-typeCa2+currentsin cerebellargranuleneuronsresistant to the subtype-specific organic and peptide Ca2+channelblockersincludemultiplechannelsubtypes
P, Q and R-type Ca2+ Currents P-type Ca2+ currents first recorded in Purkinje neurons high sensitivity to the spider toxin -agatoxin IVA Q-type Ca2+ currents first recorded in cerebellar granule neurons blocked by -agatoxin IVA with lower affinity R-type Ca2+ currents in cerebellar granule neurons resistant to the subtype-specific organic and peptide Ca2+ channel blockers include multiple channel subtypes
Voltagedependent Ca2+channels (VDCC)familymatching percentageP111120804060100Ca,1.1L-typeCa,1.2Ca,1.3HVACa,1.4Ca,2.1neuronalCa,2.2Ca,2.3Ca,3.1LVAT-typeCa,3.2Ca,3.3
Voltage dependent Ca2+ channels (VDCC) family