RESPONSIVENESS OF CARDIAC NA-DIRECTED ANTISERUM AGAINST THE CYTOSOLICLINKER BETWEEN DOMAIN-III AND DOMAIN-IV AND THEIR SENSITIVITY TO OTHER MODIFYING AGENTS( CHANNELS TO A SITE)

Elementary Na+ currents were recorded in inside-out patches from neona tal rat heart cardiocytes to analyze the influence of a site-directed polyclonal anti-serum against the linker region between the domains II I 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 (-)-en antiomer of DPI 201-106. Anti-SLP 1 serum (directed against amino acid s 1490-1507) evoked, usually within 10-15 min after cytosolic administ ration, modified Na+ channel activity. Antiserum-modified Na+ channels retain a single open state but leave, at -60 mV for example, their co nducting configuration consistently with an about threefold lower rate than normal Na+ channels. Another outstanding property of noninactiva ting Na+ channels, enhanced burst activity, may be quite individually pronounced, a surprising result which is difficult to interpret in ter ms of structure-function relations. Removal of inactivation led to an increase of reconstructed peak I(Na) (indicating a rise in NP(o)) and changed I(Na) decay to obey second-order kinetics, i.e., open probabil ity 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 a t the same membrane potential with different rates. Iodate-modified Na + channels exhibit very similar properties including a conserved condu ctance. They are likewise controlled by an efficient, voltage-dependen t deactivation process. Modification by (-)-DPI 201-106 fundamentally contrasts to the influence of anti-SLP 1 serum and the protein reagent iodate since (-)-DPI-modified Na+ channels maintain their open probab ility for at least 120 msec, i.e., a deactivation process seems lackin g. This functional difference suggests that the linker region between the domains III and IV of the alpha-subunit may not be the only target for (-)-DPI 201-106 and related compounds, if at all.