鈣與信號傳導

IntracellularCa2+SignalingDepartmentofPhysiologyBengbumedicalcollege血Ca2+濃度與Ca2+的轉(zhuǎn)運血漿Ca2+濃度正常維持在8.5-11.1mg％之間，其中46％與血漿蛋白特別是白蛋白結(jié)合，47.5％為游離鈣(Ca2+)，僅有6.5％的鈣以磷酸鈣、檸檬酸鈣、重碳酸鈣、酒石酸鈣、棕櫚酸鈣等復合物形式存在。歷史回顧1883年,Ringer(英)發(fā)現(xiàn)Ca2+是維持心跳的必要條件;1953年,Heillbrunn(美)和Kamada(日)用電生理技術(shù)提出Ca影響細胞的功能;1970年,張槐耀發(fā)現(xiàn)鈣調(diào)蛋白(Calmodulin);1978年,Neher和Sakmann建立了膜片鉗技術(shù),使單通道電流記錄成為現(xiàn)實;1985年,Tsien(美)合成了Fura-2熒光探針;可監(jiān)測胞漿游離Ca的瞬間變化;為什麼選擇Ca2+作為第二信使？Why?SocellscanraisetheirinternalCa2+quickly,andthendecreaseitquickly.Thus,canuseCa2+asanintracellularsignallingmessenger,whileavoidingtoxiceffects.一、Ca2+成為胞內(nèi)信使的基礎Ca2+胞內(nèi)外或胞質(zhì)與胞內(nèi)鈣庫的濃度差細胞外鈣：10000倍于細胞內(nèi)游離鈣。

[Ca2+]o=1~10mmol/l=10-3~10-2mol/l細胞內(nèi)鈣：游離鈣：

0.1%[Ca2+]i=100nmol/l=10-7mol/l

儲備鈣：99.9%

與蛋白質(zhì)或小分子量的有機配體結(jié)合大部分儲存于鈣庫(內(nèi)質(zhì)網(wǎng)，肌質(zhì)網(wǎng)）細胞內(nèi)總鈣濃度約為lmmol／L50％存在于細胞核線粒體占30％，濃度為0.6mmol／L內(nèi)質(zhì)網(wǎng)占14％，約0.28mmoI／L質(zhì)膜(外層)占5％，約0.1mmol／L而細胞溶質(zhì)中僅占總鈣的0.5％(結(jié)合態(tài))或0.005％(離子態(tài))胞內(nèi)鈣的分布BerridgeMJetal.,Nature.1998;395:645-648.

Ca2+–alifeanddeathsignal參與神經(jīng)肌肉的反應過程;鎮(zhèn)靜作用：缺鈣可引起神經(jīng)的興奮性增高;調(diào)節(jié)細胞功能，激活蛋白激酶，促進蛋白質(zhì)磷酸化;促進內(nèi)、外分泌腺的分泌，神經(jīng)遞質(zhì)的釋放;血液凝固;維持細胞膜的通透性及完整性;參與免疫反應。Ca2+的生理功能Calciuminmuscle:ICa的生理作用Calciumin

phototransductionCalciumintastereceptorsCalciumandsynapses:ICalciumandsynapses:II內(nèi)皮舒張因子（EDRF）≈NO：FundamentalrolesofCa2+innervecellsChargecarrier membranepotentialCellmotility

axonalguidanceSecretion neurotransmitterreleaseRegulationofgeneexpression differentiation,synapticplasticityNeuronalviability apoptosis

--是刺激誘發(fā)產(chǎn)生的級鏈反應

--通過激活蛋白激酶，引起生理功能改變或基因表達

--不是通過酶促反應生成

--與鈣結(jié)合蛋白結(jié)合而啟動不同的信息通路

--信號的產(chǎn)生和終止以胞內(nèi)鈣濃度為基礎。二、Ca2+作為第二信使與其它信使異同：Ca2+gradientunderrestingcondition[Ca2+]o10-3M[Ca2+]i10-7M

Why?1.SarcolemmaimpermeabletoCa2+

Ca2+pump(Ca2+-ATPase)Na+-Ca2+exchanger2.Endoplasmic/sarcoplasmicreticulum(ER/SR)

Ca2+-ATPase3.MitochondriaInitiationofintracellularCa2+signal[Ca2+]o10-3M[Ca2+]i10-7M

HOW?Twoprimarysources:1.External

ExtracellularCa2+2.InternalER/SR[Ca2+]i10-5MCa2+influxfromextracellularfluidthrough:(1)VOC:voltage-operatedCa2+channels(2)ROC:receptor-operatedCa2+channels(3)SOC:store-operatedCa2+channels(4)Na+-Ca2+exchanger

1.External(2)ROC (1)VOCTypesofVOC:

(1)L-type(long-lasting)(美.耶魯大學,Nowycky,1985)(2)T-type(transient)(Nowycky,1985)(3)N-type(neitherL-typenorT-type)(Nowycky,1985)(4)P-type(Purkinje)(Llinas,1992)(5)F-type(fetal)(Tohse,1992)Voltage-GatedCalciumChannels

Ca2+channelsDurationofcurrent long-lasting transientActivationkinetics slower faster Inactivationkinetics slower fasterThreshold

high(-35mV) Low(-60mV)cAMP/cGMP-regulated Yes NoPhosphorylation-regulated Yes NoOpeners Bay-K-8644 -Blockers varapamil Tetramethrin nifedipine,diltiazem Ni2+

Inactivationby[Ca2+]i Yes slightPatch-clamprecording run-down relativelystableL-type T-type

L-typeCa2+

channelPKAphosphorylationRegulationofL-typeCa2+channels:Increasesin: number probability opentime2.InternalCa2+releasefromER/SR內(nèi)質(zhì)網(wǎng)/肌漿網(wǎng)Ryanodinereceptor(2)IP3receptor(1)Ryanodinereceptor(RyR): mediatestheeffluxofCa2+

fromtheSRandplaysacentralroleinexcitation-contraction(E-C)coupling.特點1.所需鈣閾值較低

1.5-2.0μM,咖啡因可降低此閾值,Mg可升高此閾值;

2.全或無的釋放為CICR正反饋介導MechanismsofE-CcouplingIsoformsofRyRRyR1:SkeletalmuscleRyR2:CardiacmuscleRyR3:Brain(Coronado,1994)

DHPR:二氫吡啶受體RYR1:蘭尼堿受體RegulationofRyRActivation:caffeine,ryanodine(nM),CICR,(Ca–inducedcalciumrelease)phosphorylation…Inhibition:ryanodine(M),rutheniumred(釕紅),Mn2+…,(2)IP3receptorpathwayIP3R1: