Modulation of single cardiac Na+ channels by cytosolic Mg++ ions.
Elementary Na+ currents were recorded in inside-out patches excised from cultured neonatal rat heart myocytes in order to study the influence of cytosolic Mg++ and other bivalent cations present at the cytoplasmic membrane surface on cardiac Na+ channel gating. Exposing the cytoplasmic membrane surface to a Mg(++)-free environment shortened the open state of cardiac Na+ channels significantly. tau open declined to 62 +/- 2% of the value obtained at 5 mmol/l Mgi++. Other channel properties including the tendency to reopen and the elementary current size either changed insignificantly within a 10% range or remained completely unchanged. An almost identical change of tau open can be caused by switching from a Mn++ (5 mmol/l) containing internal solution to a Mn(++)-free internal solution. But tau open failed to significantly respond to a variation in internal Ni++ from 5 mmol/l to 0 mmol/l. The same response to internal Mg++ withdrawal was obtained with (-)-DPI-modified, non-inactivating Na+ channels, indicating that the exit rate from the open state remains as sensitive to cytosolic Mg++ variations as in normal Na+ channels with operating inactivation.
Benz
I
I
Physiologisches Institut, Universität Freiburg, Federal Republic of Germany.
Kohlhardt
M
M
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D015640:Ion Channel Gating; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*
D015222:Sodium Channels; D008274:Magnesium