L-type Ca-channels: similar Q10 of Ca-, Ba- and Na-conductance points to the importance of ion-channel interaction.
The temperature-dependence of currents through L-type Ca-channels was studied in myocytes isolated from the urinary bladder of the guinea pig. Currents were measured at 22 degrees C and 35 degrees C with Ca-, Ba- and Na-ions as charge carrier. The higher temperature increased the open channel conductance for Ca-ions from 8.5 to 16 pS (Q10 = 1.63 +/- 0.07, mean +/- S.D.), for Ba-ions from 24 to 43 pS (Q10 = 1.55 +/- 0.06), and for Na-ions (pH 9) from 74 to 131 pS (Q10 of 1.55 +/- 0.09). The differences in the Q10's are not significant, the activation energy approximates a common high value of 34.8 +/- 2.5 kJ/mol. A three barrier model with intra-channel binding predicts high Q10's for Ca and Ba but not for Na. To fit the results we postulate that the temperature-dependence reflects multiple ion-channel interactions within a central permeability barrier, e.g. polar groups substituting part of the ionic water shell.
Klöckner
U
U
Department of Physiology, University of Cologne, Köln, Federal Republic of Germany.
Schiefer
A
A
Isenberg
G
G
D000818:Animals; D001464:Barium / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D004594:Electrophysiology; D015640:Ion Channel Gating; D012964:Sodium / Q000502:physiology*; D013696:Temperature
D015220:Calcium Channels; D001464:Barium; D012964:Sodium; D002118:Calcium