Isoprenaline: A Potential Contributor in Sick Sinus Syndrome—Insights from a Mathematical Model of the Rabbit Sinoatrial Node

Table 2

Actions of Iso on currents.

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Increase of L-type Ca²⁺ current

 𝑖_Ca,𝐿=1+𝑓_Ca,max[Iso]𝐾_0.5,Ca′+[Iso]×𝑔_Ca,𝐿𝑓_𝐿𝑑_𝐿+0.0061+𝑒^{−(𝑉+14.1)/6}(𝑉−𝐸_Ca,𝐿)6

Shift of the activation curve of hyperpolarization-activated current

 𝑦_∞=𝑒^{−(𝑉+78.91−𝑆𝑓)/26.2}𝑒^{−(𝑉+78.91−𝑆𝑓)/26.2}+𝑒^{(𝑉+75.131−𝑆𝑓)/21.25},  𝜏_𝑦=1000.0𝑒^{−(𝑉+78.91−𝑆𝑓)/26.2}+𝑒^{(𝑉+75.131−𝑆𝑓)/21.25} 

 𝑑𝑦=𝑦𝑑𝑡^∞−𝑦𝜏_𝑦,  𝑆_𝑓=𝑆_𝑓,max[Iso]^𝑛′𝑓𝐾^𝑛′𝑓_0.5,𝑓′+[Iso]^𝑛′𝑓

Actions on rapid delayed rectifying K⁺ current

 𝑖_K,𝑟=1+𝑓_K,max[Iso]𝐾_0.5,𝑔K+[Iso]×𝑔_K,𝑟[(1−𝐹_K,𝑟)𝑝_𝑎,𝑓+𝐹_K,𝑟𝑝_𝑎,𝑠]𝑝_𝑖(𝑉−𝐸_K) 

 𝑑𝑝_𝑎,𝑓=𝑑𝑡1/1+𝑒^{−(𝑉+14.2−𝑆K)/10.6}−𝑝_𝑎,𝑓𝜏_{𝑝𝑎,𝑓},  𝑑𝑝_𝑎,𝑠=𝑑𝑡1/1+𝑒^{−(𝑉+14.2−𝑆K)/10.6}−𝑝_𝑎,𝑠𝜏_{𝑝𝑎,𝑠} 

 𝑆_K=𝑆_K,max[Iso]𝐾_0.5,Kacti+[Iso],  𝑑𝑝_𝑖=𝑑𝑡1/1+𝑒^{(𝑉+18.6)/10.1}−𝑝_𝑖1−𝑑_{𝜏K,𝑟,max}[Iso]/𝐾_{0.5,𝜏K,𝑟}+[Iso]×𝜏_𝑝𝑖

Increase of slow delayed rectifying K⁺ current

 𝑖_K,𝑠=1+𝑓_K,max[Iso]𝐾_0.5,𝑔K+[Iso]×𝑔_K,𝑠𝑥²_𝑠𝑉−𝐸_K,𝑠

Increase of sustained inward current

 𝑖_st=1+𝑓_st,max[Iso]𝐾_0.5,st+[Iso]×𝑔_st𝑞_𝑛𝑞_𝑖𝑉−𝐸_st

Actions on Ca²⁺ handling

 𝑗_up=1−𝛽_Iso×𝑃_up[Ca²⁺]_𝑖/𝐾_mf^𝑛up−[Ca²⁺]_up/𝐾_mr^𝑛up1+[Ca²⁺]_𝑖/𝐾_mf^𝑛up−[Ca²⁺]_up/𝐾_mr^𝑛up

  𝑗_rel=1+𝛼_Iso×𝑘_𝑠𝑂[Ca²⁺]_rel−[Ca²⁺]_sub

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