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)
W. Beck et al., 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), The Journal of membrane biology, 134(3), 1993, pp. 231-239
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.