Figure 3.
Identification of VDCCs in UBCs. A, The average I–V curves for the FINC component (Fast inact.; right, open circles) and for the SLINC component (Slowly inact.; right filled circles) from several cells are depicted. I–V curves were obtained by stepping the membrane potential of UBCs to Vtest for 550 ms after a 1-s-long deinactivating pulse to −100 mV. Sweep extracts from the I–V curve of one cell are illustrated on the left. Test potentials are indicated at the left of the corresponding sweeps. In this cell, the peak FINC was 890 pA at −30 mV, whereas the peak SLINC was 231 pA at −20 mV. Note the different dependence on the membrane potential of the two VDCC components. B, Bar graphs summarizing the results of the pharmacological analysis of FINC (top graph) and SLINC (bottom graph) in voltage-clamped UBCs. On the right, traces from three distinct UBCs illustrating the typical effect of replacing external calcium with cobalt (top traces), of bath application of mibefradil (middle traces), and BAYK8644 (bottom traces) are shown. Control traces are black, and traces recorded during drug application are gray. Note that cobalt completely inhibited both components (FINC, 3.4% of control; SLINC, 1.1%), whereas mibefradil strongly reduced FINC (12.8%) and, to a lesser extent, SLINC (75.3%). Finally, BAYK8644 potentiated SLINC (167.0%) while modifying FINC only slightly (118.2%). Cd, Cadmium; Ni, nickel; Co, cobalt; Mibe, mibefradil; Nimo, nimodipine; BAYK, BAYK8644. C, Single-cell RT-PCR testing the expression of VDCC mRNAs in UBCs. Left, Expression pattern for one UBC. In this case, the mRNAs of several VDCCs were amplified and revealed. Exceptions were the mRNAs of the α1B subunit-containing N-type channel and the α1I subunit-containing T-type channel. The first column on the left corresponds to molecular weight markers. Right, Bar graphs representing the number of UBCs, of a total of 21, in which the mRNAs of the indicated α1 subunits were revealed.