Manipulation of cellular excitability by cell fusion - Effects of rapid introduction of transient outward K+ current on the guinea pig action potential

To investigate the still-undetermined role of :the Ca2+-independent transie nt outward current (I-to1) on repolarization of the cardiac action potentia l, we used cell fusion to introduce I-to1 into guinea pig cardiomyocytes, w hich normally lack this current.:This technique enables the rapid delivery of premade functional ion channels to cardiomyocytes within hours of isolat ion, thus eliminating the action potential-alterations that complicate prol onged cell culture. Chinese hamster ovary(CHO) cells stably expressing Kv4. 3:(CHO-Kv4.3)- were loaded with a fluorescent dye and fused to guinea pig c ardiomyocytes using polyethylene glycol, As controls; nontransfected CHO ce lls were fused using the same protocol. Myocytes fused with CHO-Kv4.3, cell s exhibited a:robust I-tol ( 16.5+/-2.6 pA/pF at +40 mV; 37 degrees C; n=19 ), whereas controls had none. I-to1 accelerated the early repolarization ve locity (r= -0.68; 3 ms after the overshoot) and progressively suppressed th e voltage of the-plateau phase (r= -0.90) with increasing I-to1 density. Re duction of the action potential duration to 50% repolarization (r= -0.76) a nd to 90% repolarization (r= -0.65) also correlated well with I-to1 density . Thus, I-to1 exerted a significant effect on the early repolarization phas e and abbreviated action potential duration. Cell fusion is a valuable and generalizable technique to introduce preformed membrane proteins into nativ e cells.