Functional expression of voltage dependent sodium channels in Xenopus oocytes injected with mRNA from neonatal or adult rat brain.
The two electrode voltage clamp technique was used to study voltage-dependent sodium currents (INa) in Xenopus laevis oocytes previously injected with mRNA extracted from adult (A) or neonatal (N, < 5 days old) rat brains. In the presence of niflumic acid (300 microM) to block endogenous Ca(2+)-activated Cl- currents, depolarizing voltage steps from a holding potential of -100 mV to various voltages elicited in both groups of oocytes fast inward sodium currents which peaked at approximately 0 mV and then slowly declined to approximately 75% of the maximum current at +40 mV. At the peak, A INa was significantly larger than N INa (296 +/- 59 nA vs. 147 +/- 32 nA). Inactivation kinetics of N INa was best fit with one exponential component whereas A INa with two exponential components. A significant difference in the voltage dependence of inactivation was found between A INa or N INa. The values of Vh were -53 +/- 0.9 mV or -59.8 +/- 0.7 mV for A INa or N INa respectively. The recovery from inactivation was fitted in both groups with two exponential functions (tau f and tau s) whose values were not significantly different. However the ratio between tau f and tau s was significantly higher for N INa comparing to A INa (5.7 vs. 2.1). TTX reversibly blocked INa. The IC50 value was 58.2 +/- 6.3 nM for A INa and 20.4 +/- 2.2 nM for N INa. These results suggest that different isoforms of TTX-sensitive, voltage-dependent sodium channel subunits are functionally expressed, may be in different proportions in oocytes injected with A or N mRNA.
Virginio
C
C
Biophysics Laboratory, International School for Advanced Studies [SISSA], Trieste, Italy.
Cherubini
E
E
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D005260:Female; D006706:Homeostasis; D007267:Injections; D007700:Kinetics; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000032:analysis / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D014982:Xenopus laevis
D012333:RNA, Messenger; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013779:Tetrodotoxin