CONDUCTANCE-VOLTAGE RELATIONS IN LARGE-CONDUCTANCE CHLORIDE CHANNELS IN PROLIFERATING L6 MYOBLASTS

Authors
Citation
O. Hurnak et J. Zachar, CONDUCTANCE-VOLTAGE RELATIONS IN LARGE-CONDUCTANCE CHLORIDE CHANNELS IN PROLIFERATING L6 MYOBLASTS, General physiology and biophysics, 13(3), 1994, pp. 171-192
Citations number
42
Categorie Soggetti
Physiology,Biophysics
ISSN journal
02315882
Volume
13
Issue
3
Year of publication
1994
Pages
171 - 192
Database
ISI
SICI code
0231-5882(1994)13:3<171:CRILCC>2.0.ZU;2-Y
Abstract
Large-conductance chloride channels (maxi-Cl channels) were studied in cultured myoblasts (L6 rat muscle cell line); in excised (inside-out) and in cell attached membrane patches using a conventional patch clam p method. The incidence of maxi-Cl channels was substantially higher i n proliferating myoballs, then in quiescent (bottom-attached) myoblast s (90% and 50% percent of examined cells, respectively). The maxi-Cl c hannels in myoballs were present both in cell attached and excised pat ches. The channel conductance at symmetric [Cl] = 150 mmol/l was 359 /- 42 pS (n = 74) in quiescent cells and 439 +/- 10 pS (n = 6) in prol iferating myoballs respectively. The conductance of the channel in qui escent cells increased with chloride concentration in symmetric NaCl r ich solutions according to Michaelis-Menten curve with the saturation limiting conductance of about 640 pS (g(max)) and K-m = 112 mmol/l. Th e shift of the reversal potential upon increasing the pipette concentr ation of NaCl from 150 to 250 mmol/l was consistent with P-Na/P-Cl = 0 .1. Neither the conductance nor the activation of the channel were dep endent on the presence of calcium ions. The bell-shaped steady state c hannel conductance-voltage relationship is asymmetric and can be fitte d by two Boltzmann equations with different V-h and k constants; -25.6 mV and -6.8 mV, respectively, for the negative side and +49.6 mV and +13.7 mV for the positive side in quiescent cells. The corresponding v alues in proliferating myoballs were as follows: -15.5 mV and -2.4 mV, respectively, for the negative side and +31.4 mV and +6.8 mV for the positive side. From the maximum slopes of the P-open versus V curves a n estimate was made of the charges for the gates that close at negativ e (3.5) or positive (1.7) potentials, respectively, in quiescent cells . The corresponding values in myoballs were 10.6 and 3.7, respectively . The probability of one gate to be open was dependent on the state of activation of the opposite gate as determined by prepulses of the opp osite polarity. The channel showed multiple (up to six) conductance le vels that may develop in a step-like manner. The onset of the full-gro wn maxi-Cl channel is fairly abrupt; it might, however, be preceded by a small conductance unit activity. It is supposed that the difference s between the quiescent myoblasts and proliferating myoballs might ref lect increased expression of maxi-Cl channels in myoballs to perform a s yet unknown role in the cell cycle and/or proliferation of the myobl asts.