Distinguishing between three classes of Ca²⁺ channel activity in sensory neurons with distinct biophysical and pharmacological profiles. Use of the dihydropyridine BayK8644 as a selective stimulator of L-type voltage-gated Ca²⁺ channels. A, unitary L-type Ca²⁺ channel activity recorded from a cell-attached patch of a guinea pig ventricular cell, using the voltage protocol indicated. By convention, downward deflections represent inward current through the channel. Left panel, in control solution, the channel displays brief openings (mode 1 activity), with occasional null (mode 0) activity. Right panel, application of 5 μM BayK8644 greatly increases open probability by inducing long-lasting openings (mode 2). Adapted from Hess et al (1984).⁶⁰ B, In recordings of macroscopic currents, 5 μM BayK8644 dramatically increases the activity of L-type Ca²⁺ channels, but not N- or T-type channels. Left panel, control single-channel current averages recorded from cell-attached patches of chick dorsal root ganglion neurons. Right panel, the same patches recorded after application of 5 μM BayK8644. Adapted from Nowycky et al (1985).⁵⁵