Identification of Ikr kinetics and drug binding in native myocytes.
Determining the effect of a compound on I (Kr) is a standard screen for drug safety. Often the effect is described using a single IC(50) value, which is unable to capture complex effects of a drug. Using verapamil as an example, we present a method for using recordings from native myocytes at several drug doses along with qualitative features of I (Kr) from published studies of HERG current to estimate parameters in a mathematical model of the drug effect on I (Kr). I (Kr) was recorded from canine left ventricular myocytes using ruptured patch techniques. A voltage command protocol was used to record tail currents at voltages from -70 to -20 mV, following activating pulses over a wide range of voltages and pulse durations. Model equations were taken from a published I (Kr) Markov model and the drug was modeled as binding to the open state. Parameters were estimated using a combined global and local optimization algorithm based on collected data with two additional constraints on I (Kr) I-V relation and I (Kr) inactivation. The method produced models that quantitatively reproduce both the control I (Kr) kinetics and dose dependent changes in the current. In addition, the model exhibited use and rate dependence. The results suggest that: (1) the technique proposed here has the practical potential to develop data-driven models that quantitatively reproduce channel behavior in native myocytes; (2) the method can capture important drug effects that cannot be reproduced by the IC(50) method. Although the method was developed for I (Kr), the same strategy can be applied to other ion channels, once appropriate channel-specific voltage protocols and qualitative features are identified.
Gene Network Sciences, 58 Charles Street, Cambridge, MA 02141, USA. qzhou@gnsbiotech.com
Qinlian
Q
Zhou
Andrew C
AC
Zygmunt
Jonathan M
JM
Cordeiro
Fernando
F
Siso-Nadal
Robert E
RE
Miller
Gregery T
GT
Buzzard
Jeffrey J
JJ
Fox
D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage; D002478:Cells, Cultured; D003198:Computer Simulation; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000378:metabolism*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008657:Metabolic Clearance Rate; D008955:Models, Cardiovascular; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D014700:Verapamil / Q000008:administration & dosage*
D000889:Anti-Arrhythmia Agents; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D014700:Verapamil; D011188:Potassium