L-TYPE CA-CHANNELS - SIMILAR Q10 OF CA-CONDUCTANCE, BA-CONDUCTANCE 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 °C and 35 °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. © 1990 Springer-Verlag.