Molecular components of transient outward potassium current in cultured neonatal rat ventricular myocytes

Abstract

We have previously reported that K_v1.4, K_v4.2, and K_v4.3 mRNAs are present in adult and neonatal rat ventricular myocytes, and that transient outward potassium current (I_to) recovers from inactivation with a slow (I_to,s) and a fast (I_to,f) time course. This study was designed to determine the molecular correlates of I_to,s and I_to,f in cultured neonatal rat ventricular myocytes (NRVM) employing dominant-negative adenoviral infections to manipulate the function of endogenous I_to-encoding K⁺ channels. Western blot data from cultured NRVM showed that K_v1.4, K_v4.2, and K_v4.3 channel proteins are present in these myocytes. The biphasic recovery from inactivation of I_to in control GFP-infected myocytes demonstrated equal contribution of I_to,s and I_to,f in NRVM. Infection of cultured NRVM with adenoviruses expressing full-length K_v1.4 or K_v4.2 genes generated currents with recovery from inactivation kinetics similar to native I_to,s and I_to,f in GFP-infected myocytes, respectively. Overexpression of dominant-negative truncated K_v1.4 transgene (K_v1.4N) caused a 51% reduction in I_to, selectively removing the slowly recovering I_to,s. Overexpression of dominant-negative K_v4.2N reduced I_to by 53% and eliminated the fast-recovering I_to,f. Our results establish that, in neonatal rat ventricular myocytes, the shaker K_v1 family (probably K_v1.4 and/or K_v1.7) underlies I_to,s, and that the shal K_v4 family (probably K_v4.2 and K_v4.3) is responsible for I_to,f.