Figure 6. Effects of dihydropyridine Ca²⁺ channel agonist, Bay K 8644 on single-channel Ca²⁺ currents.

A Single-channel Ba²⁺ current traces were recorded in the cell-attached mode using 50 mM Ba²⁺ as the charge carrier. The traces were generated by holding the membrane patch at −70 mV and stepped to potentials indicated above each set of traces. The continuous dotted lines indicate the closed level and the downward steps indicate the opened level. Brief openings were more frequent than long openings in the unmodified channel. B Illustration of the effects of 5 μM Bay K8644 on the same patch as it is shown in A. Bay K 8644 promoted long openings. Whereas Bay K 8644 increased the frequency and duration of single-channel openings, nimodipine (10 μM) had the opposite effect (data not shown). C An example of amplitude histogram used to determine the mean magnitude of unitary currents at different step potential is shown. D Single-channel conductance (●) of L-type channel for Ba²⁺ was determined using linear least square fits to the mean single-channel amplitude at different step potentials. The conductance of the L-type channel was 22 ± 3 pS (n = 11).