Responsiveness of cardiac Na+ channels to a site-directed antiserum against the cytosolic linker between domains III and IV and their sensitivity to other modifying agents.

Elementary Na+ currents were recorded in inside-out patches from neonatal rat heart cardiocytes to analyze the influence of a site-directed polyclonal anti-serum against the linker region between the domains III and IV (amino acids 1489-1507 of the cardiac Na+ channel protein) on Na+ channel gating and to test whether this part of the alpha-subunit may be considered as a target for modifying agents such as the (-)-enantiomer of DPI 201-106. Anti-SLP 1 serum (directed against amino acids 1490-1507) evoked, usually within 10-15 min after cytosolic administration, modified Na+ channel activity. Antiserum-modified Na+ channels retain a single open state but leave, at -60 mV for example, their conducting configuration consistently with an about threefold lower rate than normal Na+ channels. Another outstanding property of noninactivating Na+ channels, enhanced burst activity, may be quite individually pronounced, a surprising result which is difficult to interpret in terms of structure-function relations. Removal of inactivation led to an increase of reconstructed peak INa (indicating a rise in NPo) and changed INa decay to obey second-order kinetics, i.e., open probability declined slowly but progressively during membrane depolarization. The underlying deactivation process is voltage dependent and responds to a positive voltage shift with a deceleration but may operate even at the same membrane potential with different rates. Iodate-modified Na+ channels exhibit very similar properties including a conserved conductance. They are likewise controlled by an efficient, voltage-dependent deactivation process.(ABSTRACT TRUNCATED AT 250 WORDS)