Expression of Ba currents in Xenopus oocyte injected with pregnant rat myometrium mRNA.

Using the single electrode voltage-clamp technique, stage V and VI Xenopus oocytes showed a Ba inward current (endogenous IBa) with a peak amplitude of -15 +/- 2 nA in a Cl and Na-free Ba methane sulphonate medium. When oocytes were injected with pregnant rat (18 days gestation) myometrium mRNA, an additional component of Ba current could be detected (exogenous IBa). This inward current could be distinguished from the native IBa by several means: i) peak amplitude (-75 +/- 3 nA); ii) activation voltage threshold; iii) steady-state inactivation parameter; iv) sensitivity to dihydropyridines. The features of the exogenous IBa were compared to those of the inward Ca channel current recorded with the tight-seal patch-clamp technique in single myometrial cells maintained in primary culture.