Résumé
Using the whole cell voltage-clamp technique and a Cl free and Na free Ba methane sulfonate solution, stage V and VI
Xenopus oocytes demonstrated a Ba current (endogenous component) with a peak amplitude average of 6 nA (6 ± 2 nA). When oocytes were injected with crustacean skeletal muscle mRNA, an additional component of I
Ba could be detected (exogenous I
Ba). The latter current could be distinguished from the native one by several electrophysiological means: a peak amplitude average of 90 nA (90 ± 4 nA), activation potential threshold, steady state inactivation properties and sensitivity to Ca blockers. As shown by Jdaïâa and Guilbault in crustacean skeletal muscle fibres, exogenous I
Ba could be divided into two components: a “fast component” and a “slow component” probably passing through two types of Ca channels (fast and slow) since the peak Ba current voltage relationship was biphasic and the fast component of exogenous I
Ba was less sensitive than the slow to nifedipine. The features of the newly synthesized channels incorporated in the
Xenopus oocyte membrane suggest that they may be associated with fast and slow channels, previously described in many preparations, particularly in crustacean skeletal muscle fibres.