Premium
The Timothy syndrome mutation of cardiac CaV1.2 (L‐type) channels: multiple altered gating mechanisms and pharmacological restoration of inactivation
Author(s) -
Yarotskyy Viktor,
Gao Guofeng,
Peterson Blaise Z.,
Elmslie Keith S.
Publication year - 2009
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2008.161737
Subject(s) - gating , mutation , mutant , chemistry , wild type , bay k8644 , agonist , biophysics , electrophysiology , cardiac action potential , medicine , endocrinology , pharmacology , biology , biochemistry , repolarization , receptor , gene
Timothy syndrome (TS) is a multiorgan dysfunction caused by a Gly to Arg substitution at position 406 (G406R) of the human CaV1.2 (L‐type) channel. The TS phenotype includes severe arrhythmias that are thought to be triggered by impaired open‐state voltage‐dependent inactivation (OS vd I). The effect of the TS mutation on other L‐channel gating mechanisms has yet to be investigated. We compared kinetic properties of exogenously expressed (HEK293 cells) rabbit cardiac L‐channels with (G436R; corresponding to position 406 in human clone) and without (wild‐type) the TS mutation. Our results surprisingly show that the TS mutation did not affect close‐state voltage‐dependent inactivation, which suggests different gating mechanisms underlie these two types of voltage‐dependent inactivation. The TS mutation also significantly slowed activation at voltages less than 10 mV, and significantly slowed deactivation across all test voltages. Deactivation was slowed in the double mutant G436R/S439A, which suggests that phosphorylation of S439 was not involved. The L‐channel agonist Bay K8644 increased the magnitude of both step and tail currents, but surprisingly failed to slow deactivation of TS channels. Our mathematical model showed that slowed deactivation plus impaired OS vd I combine to synergistically increase cardiac action potential duration that is a likely cause of arrhythmias in TS patients. Roscovitine, a tri‐substituted purine that enhances L‐channel OS vd I, restored TS‐impaired OS vd I. Thus, inactivation‐enhancing drugs are likely to improve cardiac arrhythmias and other pathologies afflicting TS patients.